Pattern forming method

ABSTRACT

A pattern forming method which uses a positive resist composition comprises: (A) a silicon-free resin capable of increasing its solubility in an alkaline developer under action of an acid; (B) a compound capable of generating an acid upon irradiation with an actinic ray or radiation; (C) a silicon-containing resin having at least one group selected from the group of consisting (X) an alkali-soluble group, (XI) a group capable of decomposing under action of an alkaline developer and increasing solubility of the resin (C) in an alkaline developer, and (XII) a group capable of decomposing under action of an acid and increasing solubility of the resin (C) in an alkaline developer, and (D) a solvent, the method comprising: (i) a step of applying the positive resist composition to a substrate to form a resist coating, (ii) a step of exposing the resist coating to light via an immersion liquid, (iii) a step of removing the immersion liquid remaining on the resist coating, (iv) a step of heating the resist coating, and (v) a step of developing the resist coating.

This is a continuation of application Ser. No. 11/655,960 filed Jan. 22,2007. The entire disclosure of the prior application is considered partof the disclosure of this accompanying continuation application and ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pattern forming method that utilizesa positive resist composition usable in a lithography process formanufacturing semiconductors, such as ICs, and circuit boards for liquidcrystal displays and thermal heads, and other photofabricationprocesses. More specifically, the invention is concerned with a patternforming method that utilizes a specified positive resist compositionsuitable for exposure performed with a projection exposure apparatus forimmersion lithography using as a light source far ultraviolet light withwavelengths of 300 nm or below.

2. Description of the Related Art

As the demand for finer semiconductor devices has grown, efforts havebeen moving ahead to develop exposure light sources having the shorterwavelengths and projection lenses having the higher numerical apertures(higher NAs). Up to the present, steppers using as light sources ArFexcimer laser with a wavelength of 193 nm and having NA of 0.84 havebeen developed. As generally well known, the resolution and the focaldepth of these machines can be given by the following expressions;

(Resolution)=k ₁·(λ/NA)

(Focal depth)=±k ₂ ·λ/NA ²

where λ is the wavelength of an exposure light source, NA is thenumerical aperture of a projection lens, and k₁ and k₂ are coefficientsconcerning a process.

Although steppers using as light sources F₂ excimer laser with awavelength of 157 nm are under study with the intention of achievinghigher resolution by further moving the exposure light sources toshorter wavelengths, it is very difficult to stabilize production costsand qualities of apparatus and materials since lens materials usable inexposure apparatus and materials usable in resist for ensuring exposureat shorter wavelengths are confined within very narrow limits, and thereis a possibility of failing to bring exposure apparatus and resisthaving sufficient performance and stability to perfection within arequired period.

As a technique of enhancing the resolution in an optical microscope, themethod of filling the space between a projection lens and a testspecimen with a liquid having a high refractive index (hereinafterreferred to as an immersion liquid), or the so-called immersion method,has hitherto been known.

This “immersion effect” can be explained as follows. In immersionlithography, the foregoing resolution and focal depth can be given bythe following expressions;

(Resolution)=k ₁·(λ₀ /n)/NA ₀

(Focal depth)=±k ₂·(λ₀ /n)/NA ₀ ²

where λ₀ is the wavelength of an exposure light in the air, n is therefractive index of an immersion liquid relative to the air and NA₀ isequal to sin θ when the convergent half angle of incident rays isrepresented by θ. That is to say, the effect of immersion is equivalentto the use of exposure light with a 1/n wavelength. In other words,application of the immersion method to a projection optical systemhaving the same NA value can multiply the focal depth by a factor of n.This technique is effective on all shapes of patterns, and besides, itcan be used in combination with super-resolution techniques under studyat present, such as a phase-shift method and an off-axis illuminationmethod.

Examples of apparatus in which this effect is applied to transfer offine circuit patterns for semiconductor devices are presented inJP-A-57-153433 and JP-A-7-220990.

Recent progress of immersion lithography is reported in Proceedings ofInternational Society for Optical Engineering (Proc. SPIE), vol. 4688,p. 11 (2002), J. Vac. Sci. Technol. B, 17 (1999), Proceedings ofInternational Society for Optical Engineering (Proc. SPIE), vol. 3999,p. 2 (2000), and WO 2004/077158. When ArF excimer laser is used as alight source, it is thought that pure water (having a refractive indexof 1.44 at 193 nm) is the most promising immersion liquid in terms ofnot only handling safety but also transmittance and refractive index at193 nm. When F₂ excimer laser is used as a light source, on the otherhand, fluorine-containing solvents have been examined with an eye tobalance between transmittance and refractive index at 157 nm, but noimmersion liquid satisfactory in terms of environmental safety andrefractive index has been found yet. From the viewpoints of the level ofimmersion effect and maturity of resist, it is thought that ArF steppersare earliest exposure apparatus equipped with immersion lithography.

From resists for KrF excimer laser (248 nm) onward, the image formingmethod referred to as chemical amplification has been adopted as amethod of patterning resists for the purpose of supplementingsensitivity drops resulting from light absorption by the resists. Toillustrate the image forming method by taking the case ofpositive-working chemical amplification, images are formed in a processthat exposure is performed to generate an acid through decomposition ofan acid generator in exposed areas, and conversion of alkali-insolublegroups into an alkali-soluble groups by utilizing the generated acid asa reaction catalyst is caused by bake after exposure (PEB: Post ExposureBake) to render the exposed areas removable with an alkaline developer.

Since application of immersion lithography to a chemical amplificationresist brings the resist layer into contact with an immersion liquid atthe time of exposure, it is indicated that the resist layer quality isaltered and ingredients having adverse effects on the immersion liquidare oozed from the resist layer. In WO 2004/068242, cases are describedwhere the resists tailored to ArF exposure suffer changes in resistperformance by immersion in water before and after the exposure, and itis pointed out that such a phenomenon is a problem in immersionlithography.

Use of chemical amplification resist in immersion lithography accordingto the foregoing general resist process in particular requires furtherimprovements in development defects appearing after development.

SUMMARY OF THE INVENTION

An object of the invention is to provide a pattern forming method whichcan ensure improvement in development defect appearing after developmentin immersion lithography.

Exemplary aspects of the invention are the following pattern formingmethods, and thereby the aforesaid object of the invention is attained.

(1) A pattern forming method which uses a positive resist compositioncomprises: (A) a silicon-free resin capable of increasing its solubilityin an alkaline developer under action of an acid; (B) a compound capableof generating an acid upon irradiation with an actinic ray or radiation;(C) a silicon-containing resin having at least one group selected fromthe group of consisting (X) an alkali-soluble group, (XI) a groupcapable of decomposing under action of an alkaline developer andincreasing solubility of the resin (C) in an alkaline developer, and(XII) a group capable of decomposing under action of an acid andincreasing solubility of the resin (C) in an alkaline developer, and (D)a solvent, the method comprising: (i) a step of applying the positiveresist composition to a substrate to form a resist coating, (ii) a stepof exposing the resist coating to light via an immersion liquid, (iii) astep of removing the immersion liquid remaining on the resist coating,(iv) a step of heating the resist coating, and (v) a step of developingthe resist coating.

(2) The pattern forming method as described in (1), wherein the resin(A) has a mononuclear or polynuclear alicyclic hydrocarbon structure.

(3) The pattern forming method as described in (1) or (2), wherein theresist coating is exposed to light of a wavelength of 193 nm.

(4) The pattern forming method as described in any of (1) to (3),further comprising a step of cleaning the resist coating surface priorto (ii) the step of exposing the resist coating to light via animmersion liquid.

(5) The pattern forming method as described in any of (1) to (4),wherein (iii) the step of removing the immersion liquid remaining on theresist coating is a step of removing the immersion liquid by feeding awater-miscible organic solvent onto the resist coating.

(6) The pattern forming method as described in (5), wherein thewater-miscible organic solvent is isopropyl alcohol.

In addition, the following are preferred embodiments of the invention.

(7) The pattern forming method as described in any of (1) to (6),wherein the silicon-containing resin (C) has a weight-average molecularweight of 1,000 to 100,000.

(8) The pattern forming method as described in any of (1) to (7),wherein the silicon-containing resin (C) further contains a fluorineatom.

(9) The pattern forming method as described in any of (1) to (8),wherein the silicon-containing resin (C) is added in an amount of 0.1 to5 mass % based on the total solids in the positive resist composition.

(10) The pattern forming method as described in any of (1) to (4) and(7) to (9), wherein (iii) the step of removing the immersion liquidremaining on the resist coating includes steps of forming a liquid film(puddle) of the immersion liquid and removing the liquid film so as notto left any liquid drops.

(11) The pattern forming method as described in (10), wherein the stepof removing the liquid film is a step of removing the liquid film whilerotating the substrate at 500 rpm or above.

(12) The pattern forming method as described in any of (1) to (11),wherein the resin (A) has a repeating unit containing a group having apolycyclic hydrocarbon structure substituted by a hydroxyl group or acyano group.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described below in detail.

Additionally, the term “group (atomic group)” used in this specificationis intended to include both unsubstituted and substituted ones whenneither word substituted nor unsubstituted is added thereto. Forinstance, the term “alkyl group” is intended to include not only analkyl group having no substituent (an unsubstituted alkyl group) butalso an alkyl group having a substituent or substituents (a substitutedalkyl group).

[1] Silicon-Free Resin (A) that can Increase Solubility in AlkalineDeveloper Under Action of Acid

One of resins used in a positive resist composition according to theinvention is a silicon-free resin that can increase solubility in analkaline developer under action of an acid, and a resin that containsgroups capable of decomposing under action of an acid to producealkali-soluble groups (hereinafter referred to as “acid-decomposablegroups” also) in either its main chain, or its side chains, or both(hereinafter referred to as “Resin (A)” also).

As examples of Resin (A), mention may be made of poly(hydroxystyrene)derivatives including polymers which each contain repeating unitsderived from styrene having a hydroxyl substituent at the meta-, para-or ortho-position as illustrated below.

Examples of an alkali-soluble group include groups respectively having aphenolic hydroxyl group, a carboxylic acid group, a fluorinated alcoholgroup, a sulfonic acid group, a sulfonamide group, a sulfonylimidegroup, an (alkylsulfonyl)(alkylcarbonyl)methylene group, an(alkylsulfonyl)(alkylcarbonyl)imide group, a bis(alkylcarbonyl)methylenegroup, a bis(alkylcarbonyl)imide group, a bis(alkylsulfonyl)methylenegroup, a bis(alkylsulfonyl)imide group, a tris(alkylcarbonyl)methylenegroup and a tris(alkylsulfonyl)methylene group.

Of these alkali-soluble groups, a carboxylic acid group, a fluorinatedalcohol group (preferably a hexafluoroisopropanol group,—C(CF₃)(CF₃)(OH)) and a sulfonic acid group are preferred over theothers.

Groups suitable as groups capable of decomposing by an acid(acid-decomposable groups) are those obtained by substituting groupscapable of splitting off under action of an acid for hydrogen atoms ofthe alkali-soluble groups as recited above.

Examples of a group capable of splitting off under action of an acidinclude groups of formula —C(R₃₆)(R₃₇)(R₃₈), groups of formula—C(R₃₆)(R₃₇)(OR₃₉), and groups of formula —C(R₀₁)(R₀₂)(OR₃₉).

In those formulae, R₃₆ to R₃₉ each represent an alkyl group, acycloalkyl group, an aryl group, an aralkyl group or an alkenyl groupindependently. R₃₆ and R₃₇ may combine with each other to form a ring.

R₀₁ and R₀₂ each represent a hydrogen atom, an alkyl group, a cycloalkylgroup, an aryl group, an aralkyl group or an alkenyl groupindependently.

Examples of a group suitable as an acid-decomposable group include cumylester groups, enol ester groups, acetal ester groups and tertiary alkylester groups. Of these groups, tertiary alkyl ester groups are preferredover the others.

It is advantageous for Resin (A) to have mononuclear or polynuclearalicyclic hydrocarbon structures.

Resin (A) is preferably a resin having at least one kind of repeatingunits selected from repeating units having partial structures containingalicyclic hydrocarbon groups represented by the following formulae (pI)to (pV) or repeating units represented by the following formula (II-AB)(hereinafter referred to as “an alicyclic hydrocarbon-containingacid-decomposable resin” also).

In the formulae (pI) to (pV), R₁₁ represents a methyl group, an ethylgroup, an n-propyl group, an isopropyl group, an n-butyl group, anisobutyl group or a sec-butyl group, and Z represents atoms forming acycloalkyl group together with the carbon atom.

R₁₂ to R₁₆ each represent a linear or branched alkyl group or acycloalkyl group independently, provided that at least one of R₁₂ toR₁₄, or either R₁₅ or R₁₆ represents a cycloalkyl group.

R₁₇ to R₂₁ each represent a hydrogen atom, a linear or branched alkylgroup or a cycloalkyl group independently, provided that at least one ofR₁₇ to R₂₁ represents a cycloalkyl group. Further, either R₁₉ or R₂₁ isrequired to represent a linear or branched alkyl group or a cycloalkylgroup.

R₂₂ to R₂₅ each represent a hydrogen atom, a linear or branched alkylgroup or a cycloalkyl group independently, provided that at least one ofR₂₂ to R₂₅ represents a cycloalkyl group. Alternatively, R₂₃ and R₂₄ maycombine with each other to form a ring.

In the formula (II-AB), R₁₁′ and R₁₂′ each represent a hydrogen atom, acyano group, a halogen atom or an alkyl group independently.

Z′ represents atoms forming an alicyclic structure together with the twobonded carbon atoms (C—C).

The formula (II-AB) is preferably the following formula (II-AB1) orformula (II-AB2).

In the formulae (II-AB1) and (II-AB2), R₁₃′ to R₁₆′ each independentlyrepresent a hydrogen atom, a halogen atom, a cyano group, —COOH, —COOR₅,a group capable of decomposing under action of an acid,—C(═O)—X-A′—R₁₇′, an alkyl group or a cycloalkyl group. At least two ofR₁₃′ to R₁₆′ may combine with each other to form a ring.

R₅ represents an alkyl group, a cycloalkyl group or a group having alactone structure.

X represents an oxygen atom, a sulfur atom, —NH—, —NHSO₂— or —NHSO₂NH—.

A′ represents a single bond or a divalent linkage group.

R₁₇′ represents —COOH, —COOR₅, —CN, a hydroxyl group, an alkoxy group,—CO—NH—R₆, —CO—NH—SO₂—R₆ or a group having a lactone structure.

R₆ represents an alkyl group or a cycloalkyl group.

n represents 0 or 1.

The alkyl group which R₁₂ to R₂₅ each can represent in the formulae (pI)to (pV) is preferably a 1-4C linear or branched alkyl group, withexamples including a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group and a sec-butylgroup.

The cycloalkyl group which R₁₂ to R₂₅ each can represent or thecycloalkyl group which can be formed of Z and the carbon atoms may bemonocyclic or polycyclic. Examples of such a cycloalkyl group includegroups each containing at least 5 carbon atoms and having a monocyclo,bicyclo, tricyclo or tetracyclo structure. The number of carbon atoms insuch a structure is preferably from 6 to 30, particularly preferablyfrom 7 to 25.

Suitable examples of such a cycloalkyl group include an adamantyl group,a noradamantyl group, a decaline residue, a tricyclodecanyl group, atetracyclododecanyl group, a norbornyl group, a cedrol group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup, a cyclodecanyl group and a cyclododecanyl group. Of these groups,an adamantyl group, a norbornyl group, a cyclohexyl group, a cyclopentylgroup, a tetradecanyl group and a tricyclodecanyl group are preferredover the others.

Each of these alkyl groups and cycloalkyl groups may further have asubstituent. Examples of such a substituent include an alkyl group(1-4C), a halogen atom, a hydroxyl group, an alkoxy group (1-4C), acarboxyl group and an alkoxycarbonyl group (2-6C). Herein, the alkyl,alkoxy and alkoxycarbonyl groups each may further have a substituent,such as a hydroxyl group, a halogen atom or an alkoxy group.

The structures represented by the formulae (pI) to (pV) in the resinscan be used for protection of alkali-soluble groups. Examples ofalkali-soluble groups which can be protected by such structures includevarious groups which are known in this technical field.

More specifically, such a protected alkali-soluble group has a structureformed by substituting the structure represented by any of the formulae(pI) to (pV) for the hydrogen atom of carboxylic acid, sulfonic acid,phenol or thiol group. Suitable examples of such a structure includestructures formed by substituting the structures represented by formulae(pI) to (pV) for the hydrogen atoms of carboxylic acid groups orsulfonic acid groups.

As repeating units having alkali-soluble groups protected by thestructures of formulae (pI) to (pV), repeating units represented by thefollowing formula (pA) are preferred.

In the formula (pA), each R represents a hydrogen atom, a halogen atomor a 1-4C linear or branched alkyl group. A plurality of Rs may be thesame or different.

A represents a single bond, an alkylene group, an ether group, athioether group, a carbonyl group, an ester group, an amide group, asulfonamide group, a urethane group, a urea group, or a combination oftwo or more of the groups recited above. A is preferably a single bond.

Rp₁ represents any of the formulae (pI) to (pV).

The most suitable of repeating units represented by the formula (pA) isa repeating unit derived from 2-alkyl-2-adamantyl (meth)acrylate ordialkyl(1-adamantyl)methyl (meth)acrylate.

Examples of a repeating unit represented by the formula (PA) areillustrated below, but these examples should not be construed aslimiting the scope of the invention.

(In the following formulae, Rx is H, CH₃, CF₃ or CH₂OH, and Rxa and Rxbare each a 1-4C alkyl group.)

Examples of a halogen atom which R₁₁′ and R₁₂′ each can represent in theformula (II-AB) include a chlorine atom, a bromine atom, a fluorine atomand an iodine atom.

Examples of an alkyl group which R₁₁′ and R₁₂′ each can representinclude 1-10C linear or branched alkyl groups.

The atomic group Z′ for forming an alicyclic structure is an atomicgroup forming a repeating unit having an alicyclic hydrocarbon structurewhich may have a substituent, particularly preferably atoms forming arepeating unit having a bridged alicyclic hydrocarbon structure.

Examples of a skeleton of the alicyclic hydrocarbon formed include thesame ones as alicyclic hydrocarbon groups which R₁₂ to R₂₅ can representin the formulae (pI) to (pV).

The skeleton of each alicyclic hydrocarbon structure may have asubstituent. Examples of such a substituent include R₁₃′ to R₁₆′ in theformula (II-AB1) or (II-AB2).

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention can contain groups capable of decomposing under action ofan acid in at least one type of repeating units chosen from repeatingunits having partial structures containing alicyclic hydrocarbonsrepresented by the formulae (pI) to (pV), repeating units represented bythe formula (II-AB) or repeating units of copolymerization componentsdescribed hereinafter.

Various kinds of substituents as R₁₃′ to R₁₆′ in the formula (II-AB1) or(II-AB2) may also become substituents of atoms Z′ forming an alicyclichydrocarbon structure or a bridged alicyclic hydrocarbon structure inthe formula (II-AB).

Examples of repeating units represented by the formulae (II-AB1) and(II-AB2) are illustrated below, but these examples should not beconstrued as limiting the scope of the invention.

It is preferable that the alicyclic hydrocarbon-containingacid-decomposable resin for use in the invention further has repeatingunits each containing a group having a lactone structure. Although thegroup having a lactone structure may be any group as far as it has alactone structure, it is preferably a group having a 5- to 7-memberedring lactone structure, far preferably one which fuses with another ringstructure to form a bicyclo or spiro structure. Of the groups havinglactone structures, the groups having lactone structures represented bythe following formulae (LC1-1) to (LC1-16) are preferred over theothers. Alternatively, the groups having lactone structures may bebonded directly to the main chain. The lactone structures used toadvantage are (LC1-1), (LC1-4), (LC1-5), (LC1-6), (LC1-13) and (LC1-14),and the use of specified lactone structures contributes to improvementsin line edge roughness and development defect.

Each lactone structure moiety may have a substituent (Rb₂) or needn't.Suitable examples of a substituent (Rb₂) include 1-8C alkyl groups, 3-7Ccycloalkyl groups, 1-8C alkoxy groups, 1-8C alkoxycarbonyl groups, acarboxyl group, halogen atoms, a hydroxyl group, a cyano group andacid-decomposable groups. n₂ represents an integer of 0 to 4. When n2 is2 or above, a plurality of Rb₂s may be the same or different, or theymay combine with each other to form a ring.

Examples of a repeating unit containing a group having a lactonestructure represented by any of the formulae (LC1-1) to (LC1-16) includethe repeating units represented by the formula (II-AB1) or (II-AB2)wherein at least one of R₁₃′ to R₁₆′ is a group having the lactonestructure represented by any of the formulae (LC1-1) to (LC1-16) (forinstance, R₅ in —COOR₅ represents a group having the lactone structurerepresented by any of the formulae (LC1-1) to (LC1-16)) and repeatingunits represented by the following formula (AI).

In the formula (A1), Rb₀ represents a hydrogen atom, a halogen atom or a1-4C alkyl group. Examples of a suitable substituent the alkyl grouprepresented by Rb₀ may have include a hydroxyl group and halogen atoms.

Examples of a halogen atom represented by Rb₀ include a fluorine atom, achlorine atom, a bromine atom and an iodine atom.

Rb₀ is preferably a hydrogen atom or a methyl group.

Ab represents a single bond, an alkylene group, a divalent linkage grouphaving a mononuclear or polynuclear alicyclic hydrocarbon structure, anether group, an ester group, a carbonyl group, or a divalent groupformed by combining two or more of the groups recited above.

Ab is preferably a single bond or a linkage group represented by-Ab₁-CO₂—. Ab₁ is a linear or branched alkylene group or a mononuclearor polynuclear cycloalkylene group, preferably a methylene group, anethylene group, a cyclohexylene group, an adamantylene group or anorbornylene group.

V represents a group having a lactone structure represented by any ofthe formulae (LC1-1) to (LC1-16).

A repeating unit having a lactone structure generally has opticalisomers, and any of the optical isomers may be used. Further, oneoptical isomer may be used by itself, or two or more of optical isomersmay be used as a mixture. When one optical isomer is mainly used, theoptical purity (ee) thereof is preferably 90 or above, far preferably 95or above.

Examples of a repeating unit containing a group having a lactonestructure are illustrated below, but these examples should not beconstrued as limiting the scope of the invention.

(In each of the following formulae, Rx is H, CH₃, CH₂OH or CF₃)

(In each of the following formulae, Rx is H, CH₃, CH₂OH or CF₃)

(In each of the following formulae, Rx is H, CH₃, CH₂OH or CF₃)

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention preferably has repeating units containing groups havingalicyclic hydrocarbon structures (preferably polycyclic hydrocarbonstructures) substituted with polar groups. By introduction of suchrepeating units in the resin, adhesiveness to a substrate and affinityfor a developer can be enhanced. Suitable examples of an alicyclichydrocarbon structure in the alicyclic hydrocarbon structure substitutedwith a polar group include an adamantyl group, a diamantyl group and anorbornyl group, and suitable examples of a polar group in such astructure are a hydroxyl group and a cyano group. As groups havingalicyclic hydrocarbon structures substituted with polar groups, thoserepresented by the following formulae (VIIa) to (VIId) are suitable.

In the formulae (VIIa) to (VIIc), R_(2C) to R_(4C) each represent ahydrogen atom, a hydroxyl group or a cyano group independently, providedthat at least one of them represents a hydroxyl group or a cyan group.Cases where one or two of R_(2C) to R_(4C) are hydroxyl groups and theremainder is a hydrogen atom are preferred. In the formula (VIIa), it isfar preferred that two of R_(2C) to R_(4C) are hydroxyl groups and theremainder is a hydrogen atom.

Examples of repeating units containing groups represented by theformulae (VIIa) to (VIId) include the repeating units represented by theformula (II-AB1) or (II-AB2) wherein at least one of R₁₃′ to R₁₆′ is agroup represented by any of the formulae (VIIa) to (VIId) (for instance,R₅ in —COOR₅ represents a group represented by any of the formulae(VIIa) to (VIId)) and repeating units represented by the followingformulae (AIIa) to (AIId).

In the formula (AIIa) to (AIId), R_(1C) represents a hydrogen atom, amethyl group, a trifluoromethyl group or a hydroxymethyl group.

Examples of repeating units represented by the formulae (AIIa) to (AIId)are illustrated below, but these examples should not be construed aslimiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention may have repeating units represented by the followingformula (VIII).

In the formula (VIII), Z₂ represents —O— or —N(R₄₁)—. R₄₁ represents ahydrogen atom, a hydroxyl group, an alkyl group or —OSO₂—R₄₂. R₄₂represent an alkyl group, a cycloalkyl group or a camphor residue. Thealkyl groups of R₄₁ and R₄₂ may be substituted with halogen atoms(preferably fluorine atoms).

Examples of a repeating unit represented by the formula (VIII) areillustrated below, but these examples should not be construed aslimiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention preferably has repeating units containing alkali solublegroups far preferably repeating units containing carboxyl groups. Bycontaining such groups in the repeating units, resolution in contacthole uses is enhanced. Suitable examples of repeating units containingcarboxyl groups include repeating units containing carboxyl groups in astate that they are bonded directly to the resin's main chain, such asrepeating units derived from acrylic acid and methacrylic acid,repeating units containing carboxyl groups in a state that they areattached to the resin's main chain via linkage groups, and polymer chainterminals wherein alkali-soluble groups are introduced by using apolymerization initiator or chain transfer agent having analkali-soluble group at the time of polymerization. Therein, the linkagegroups may have mononuclear or polynuclear cyclic hydrocarbonstructures. However, repeating units derived from acrylic acid andmethacrylic acid in particular are preferred.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention may further contain repeating units which each have one,two or three groups represented by the following formula (F1). Bycontaining such repeating units, line edge roughness can be improved.

In the formula (F1), R₅₀ to R₅₅ each represent a hydrogen atom, afluorine atom or an alkyl group independently, provided that at leastone of R₅₀ to R₅₅ is a fluorine atom or a fluorinated alkyl groupobtained by substituting at least one hydrogen atom with a fluorineatom.

Rxa represents a hydrogen atom or an organic group (preferably anacid-decomposable protective group, an alkyl group, a cycloalkyl group,an acyl group or an alkoxycarbonyl group).

The alkyl group represented by each of R₅₀ to R₅₅ may be substitutedwith a halogen atom, such as a fluorine atom, or a cyano group, withsuitable examples including 1-3C alkyl groups, such as a methyl groupand a trifluoromethyl group.

The case where all of R₅₀ to R₅₅ are fluorine atoms is preferred.

Suitable examples of an organic group represented by Rxa include anacid-decomposable protective group, and substituted or unsubstitutedalkyl, cycloalkyl, acyl, alkylcarbonyl, alkoxycarbonyl,alkoxycarbonylmethyl, alkoxymethyl and 1-alkoxyethyl groups.

The repeating units having groups represented by the formula (F1) arepreferably repeating units represented by the following formula (F2).

In the formula (F2), Rx represents a hydrogen atom, a halogen atom or a1-4C alkyl group. Suitable examples of a substituent the alkyl group asRx may have include a hydroxyl group and halogen atoms.

Fa represents a single bond or a linear or branched alkylene group(preferably a single bond).

Fb represents a mononuclear or polynuclear cyclic hydrocarbon group.

Fc represents a single bond or a linear or branched alkylene group(preferably a single bond or a methylene group).

F₁ represents a group represented by the formula (F1).

P₁ represents 1 to 3.

The cyclic hydrocarbon group as Fb is preferably a cyclopentylene group,a cyclohexylene group or a norbornylene group.

Examples of a repeating unit having a group represented by the formula(F1) are illustrated below, but these examples should not be construedas limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention may further contain repeating units having alicyclichydrocarbon structures but not showing acid decomposability. Byintroduction of such repeating units, elution of low molecularcomponents from a resist coating into an immersion liquid at the time ofperformance of immersion lithography can be reduced. Examples of suchrepeating units include those derived from 1-adamantyl (meth)acrylate,tricyclodecanyl (meth)acrylate and cyclohexyl (meth)acrylate.

In addition to the repeating structural units recited above, thealicyclic hydrocarbon-containing acid-decomposable resin for use in theinvention can contain a wide variety of repeating structural units forthe purpose of controlling resistance to dry etching, suitability forstandard developers, adhesiveness to substrates, resist profile, andbesides, characteristics generally required for resist, such asresolution, thermal resistance and sensitivity.

Examples of such repeating structural units include repeating structuralunits corresponding to the monomers as recited below, but these examplesshould not be construed as limiting the scope of the invention.

By containing those repeating units, it becomes possible to make fineadjustments to properties required for the alicyclichydrocarbon-containing acid-decomposable resin, especially to:

(1) solubility in coating solvents,(2) film formability (glass transition temperature),(3) alkali developability,(4) thinning of film (hydrophilic-hydrophobic balance, alkali-solublegroup selection),(5) adhesion of unexposed areas to a substrate, and(6) dry etching resistance.

Examples of monomers suitable for the foregoing purposes includecompounds which each have one addition-polymerizable unsaturated bondand are selected from acrylic acid esters, methacrylic acid esters,acrylamides, methacrylamides, allyl compounds, vinyl ethers or vinylesters.

In addition to those monomers, any other monomers may be copolymerizedso long as they are addition-polymerizable unsaturated compounds capableof forming copolymers together with monomers corresponding to thevarious repeating structural units mentioned above.

The mole fraction of each repeating structural unit in the alicyclichydrocarbon-containing acid-decomposable resin can be chosenappropriately for adjusting dry etching resistance, standard developersuitability, adhesion to substrates, resist profile, and characteristicsgenerally required for resist, such as resolution, thermal resistanceand sensitivity.

Examples of a preferred state of the alicyclic hydrocarbon-containingacid-decomposable resin for use in the invention include the following.

(1) A state of containing repeating units each having a partialstructure containing an alicyclic hydrocarbon represented by any of theformulae (pI) to (pV) (sid-chain-type).

The repeating units contained therein are preferably (meth)acrylaterepeating units each having a structure containing any of (pI) to (pV).

(2) A state of containing repeating units represented by the formula(II-AB) (main-chain type). However, the state (2) further includes thefollowing.

(3) A state of having repeating units represented by the formula (II-AB)and maleic anhydride derivative and (meth)acrylate structures (hybridtype).

The content of repeating units having acid-decomposable groups in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably10 to 60 mole %, far preferably 20 to 50 mole %, further preferably 25to 40 mole %, of the total repeating structural units.

The content of repeating units having partial structures containingalicyclic hydrocarbons represented by the formulae (pI) to (pV) in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably20 to 70 mole %, far preferably 20 to 50 mole %, further preferably 25to 40 mole %, of the total repeating structural units.

The content of repeating units represented by the formula (II-AB) in thealicyclic hydrocarbon-containing acid-decomposable resin is preferably10 to 60 mole %, far preferably 15 to 55 mole %, further preferably 20to 50 mole %, of the total repeating structural units.

The content of repeating structural units derived from the additionalcomonomers in the resin can also be chosen appropriately according tothe intended resist performance. In general, the proportion of suchrepeating structural units is preferably 99 mole % or below, farpreferably 90 mole % or below, further preferably 80 mole % or below,based on the total mole number of the repeating structural units havingpartial structures containing alicyclic hydrocarbons represented by theformulae (pI) to (pV) and the repeating units represented by the formula(II-AB).

When the composition according to the invention is designed for ArFexposure use, it is appropriate to adopt resins not having any aromaticgroups in point of transparency to ArF light.

As to the alicyclic hydrocarbon-containing acid-decomposable resin foruse in the invention, all of its repeating units are preferablyconstituted of (meth)acrylate repeating units. Herein, all the repeatingunits may be either acrylate repeating units alone, or methacrylaterepeating units alone, or a mixture of acrylate and methacrylaterepeating units. However, it is preferable that the acrylate repeatingunits is at most 50 mole % of the total repeating units. And it is farpreferable that the alicyclic hydrocarbon-containing acid-decomposableresin is a ternary copolymer containing 20 to 50 mole % of repeatingunits having partial structures containing alicyclic hydrocarbonsrepresented by any of the formulae (pI) to (pV), 20 to 50 mole % ofrepeating units containing lactone structures and 5 to 30 mole % ofrepeating units having alicyclic hydrocarbon structures substituted withpolar groups, or a quaternary copolymer further containing 0 to 20 mole% of other repeating units.

The resin preferred in particular is a ternary copolymer containing 20to 50 mole % of repeating units having acid-decomposable groups, whichare represented by any of the following formulae (ARA-1) to (ARA-5), 20to 50 mole % of repeating units having lactone groups, which arerepresented by any of the following formulae (ARL-1) to (ARL-6), and 5to 30 mole % of repeating units having alicyclic hydrocarbon structuressubstituted with polar groups, which are represented by any of thefollowing formulae (ARH-1) to (ARH-3), or a quaternary copolymer furthercontaining 5 to 20 mole % of either repeating units having carboxylgroups, or repeating units having structures represented by the formula(F1), or repeating units having alicyclic hydrocarbon structures but notshowing acid decomposability.

In the above concrete examples each, Rxy₁ represents a hydrogen atom ora methyl group.

Rxa₁ and Rxb₁ each represent a methyl group or an ethyl groupindependently.

The alicyclic hydrocarbon-containing acid-decomposable resin preferablyhas repeating units represented by the following formula (A1), repeatingunits represented by the following formula (A2) and repeating unitsrepresented by the following formula (A3).

In the formulae (A1) to (A3), Xa, Xb and Xc each represent a hydrogenatom or a methyl group independently.

R₁ represents a univalent organic group having a lactone structure.

R₂ represents a univalent organic group having a hydroxyl group or acyano group.

R₃ represents a group capable of splitting off under action of an acid.

The repeating units represented by the formula (A1) are preferably therepeating units represented by the formula (AI) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A1) ispreferably 25 to 50 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The repeating units represented by the formula (A2) are preferably therepeating units represented by the formula (AIIa) or (AIIb) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A2) ispreferably 5 to 30 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The repeating units represented by the formula (A3) are preferably therepeating units represented by the formula (pA) illustratedhereinbefore.

The proportion of the repeating units represented by the formula (A3) ispreferably 25 to 50 mole % of the total repeating units in the alicyclichydrocarbon-containing acid-decomposable resin.

The alicyclic hydrocarbon-containing acid-decomposable resin for use inthe invention can be synthesized according to general methods (e.g.,radical polymerization). As examples of a general synthesis method,there are known a batch polymerization method in which polymerization iscarried out by dissolving monomer species and an initiator in a solventand heating, and a drop polymerization method in which a solutioncontaining monomer species and an initiator is added dropwise to aheated solvent over 1 to 10 hours. However, it is preferable to use thedrop polymerization method. Examples of a solvent usable in thepolymerization reaction include ethers, such as tetrahydrofuran,1,4-dioxane and diisopropyl ether; ketones, such as methyl ethyl ketoneand methyl isobutyl ketone; ester solvents, such as ethyl acetate; amidesolvents, such as dimethylformamide and dimethylacetamide; and solventsdescribed later in which the present composition can be dissolved, suchas propylene glycol monomethyl ether acetate, propylene glycolmonomethyl ether and cyclohexanone. Further, it is preferred to performpolymerization by use of the same solvent as used in the present resistcomposition. By doing so, development of particles during storage can beretarded.

The polymerization reaction is preferably carried out in an atmosphereof inert gas, such as nitrogen or argon. And the polymerization isinitiated using a commercially available radical initiator (e.g., anazo-type initiator or peroxide) as polymerization initiator. As theradical initiator, an azo-type initiator is suitable, and an azo-typeinitiator having an ester group, a cyano group or a carboxyl group ispreferable. Examples of such a preferable azo-type initiator includeazobisisobutyronitrile, azobisdimethylvaleronitrile and dimethyl2,2′-azobis(2-methylpropionate). Such an initiator may be addedadditionally in the course of polymerization as required, or may beadded in several portions. After the conclusion of the reaction, thereaction solution is poured into a solvent, and the intended polymer iscollected as a powder or a solid. The concentration of a reaction systemis from 5 to 50 mass %, preferably from 10 to 30 mass %, and thereaction temperature is generally from 10° C. to 150° C., preferablyfrom 30° C. to 120° C., far preferably from 60° C. to 100° C.

As to Resin (A), the weight-average molecular weight thereof ispreferably from 1,500 to 100,000, far preferably from 2,000 to 70,000,particularly preferably from 3,000 to 50,000. The dispersion degreethereof is preferably from 1.0 to 3.0, far preferably from 1.0 to 2.5,further preferably from 1.0 to 2.0.

The addition amount of Resin (A) is from 50 to 99.7 mass %, preferablyfrom 70 to 99.5 mass %, of the total solids in the positive resistcomposition.

[2] Compound (B) that can Generate Acid upon Irradiation with ActinicRay or Radiation

The positive resist composition according to the invention contains acompound capable of generating an acid upon irradiation with an actinicray or radiation (which is also referred to as “an acid generator”).

The compound usable as such an acid generator can be selectedappropriately from photo-initiators for cationic photopolymerization,photo-initiators for radical photopolymerization, photodecoloring agentsfor dyes, photodiscoloring agents, compounds used in microresists andknown to generate acids upon irradiation with an actinic ray orradiation, or mixtures of two or more thereof.

Examples of such compounds include diazonium salts, phosphonium salts,sulfonium salts, iodonium salts, imide sulfonates, oxime sulfonates,diazodisulfone, disulfone and o-nitrobenzylsulfonate.

In addition, polymeric compounds having those groups or compoundscapable of generating acids upon irradiation with an actinic ray orradiation in a state of being introduced in their main or side chainscan also be used. Examples of such polymeric compounds include thecompounds as disclosed in U.S. Pat. No. 3,849,137, German Patent No.3914407, JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038,JP-A-63-163452, JP-A-62-153853 and JP-A-63-146029.

Further, the compounds capable of generating acids by the action oflight as disclosed in U.S. Pat. No. 3,779,778 and European Patent No.126,712 can also be used.

Of the compounds capable of decomposing upon irradiation with an actinicray or radiation to generate acids, compounds represented by thefollowing formulae (ZI), (ZII) and (ZIII) respectively are preferred.

In the formula (ZI), R₂₀₁, R₂₀₂ and R₂₀₃ each represent an organic groupindependently.

X⁻ represents a non-nucleophilic anion, preferably a sulfonic acidanion, a carboxylic acid anion, a bis(alkylsulfonyl)amide anion, atris(alkylsulfonyl)methide anion, BF₄ ⁻, PF₆ ⁻ or SbF₆ ⁻, far preferablyan organic anion having at least one carbon atom.

Examples of an organic anion suitable as X⁻ include organic anionsrepresented by the following formulae.

In the above formulae, Rc₁ represents an organic group.

Examples of an organic group as Rc₁ include those containing 1 to 30carbon atoms, preferably alkyl groups and aryl groups, which each may besubstituted, and groups formed by connecting two or more of those groupsvia one or more of linkage groups, such as a single bond, —O—, —CO₂—,—S—, —SO₃— and —SO₂N(Rd₁)—. Rd₁ represents a hydrogen atom or an alkylgroup.

Rc₃, Rc₄ and Rc₅ each represents an organic group independently.Suitable examples of such an organic group include the same organicgroups as recited as those preferred by Rc₁, especially 1-4Cperfluoroalkyl groups.

Rc₃ and Rc₄ may combine with each other to form a ring. The group formedby combining Rc₃ with Rc₄ is an alkylene group or an arylene group,preferably a 2-4C perfluoroalkylene group.

The organic groups particularly preferred as Rc₁ and Rc₃ to Rc₅ arealkyl groups substituted with fluorine atoms or fluoroalkyl groups attheir respective 1-positions and phenyl groups substituted with fluorineatoms or fluoroalkyl groups. When a fluorine atom or a fluoroalkyl groupis present, the acid generated by irradiation with light can have highacidity to result in enhancement of the sensitivity. On the other hand,when Rc₃ and Rc₄ combine with each other to form a ring, the acidgenerated by irradiation with light can also increase its acidity toresult in enhancement of the sensitivity.

The number of carbon atoms in the organic group as R₂₀₁, R₂₀₂ and R₂₀₃each is generally from 1 to 30, preferably from 1 to 20.

Two of R₂₀₁ to R₂₀₃ may combine with each other to form a ringstructure, and the ring formed may contain an oxygen atom, a sulfuratom, an ester linkage, an amide linkage or a carbonyl group. Examplesof a group formed by combining two of R₂₀₁, R₂₀₂ and R₂₀₃ includealkylene groups (such as a butylene group and a pentylene group).

Examples of organic groups as R₂₀₁, R₂₀₂ and R₂₀₃ include theircorresponding groups in compounds (Z1-1), (Z1-2) and (Z1-3) illustratedbelow.

Additionally, the acid generator may be a compound having two or more ofstructures represented by formula (ZI). For instance, the acid generatormay be a compound having a structure that at least one of R₂₀₁, R₂₀₂ andR₂₀₃ in one compound represented by formula (ZI) is bound to at leastone of R₂₀₁, R₂₀₂ and R₂₀₃ in another compound represented by formula(ZI).

Examples of a further preferred component (ZI) include compounds (ZI-1),(ZI-2) and (ZI-3).

The compound (Z1-1) is an arylsulfonium compound represented by theformula (ZI) wherein at least one of R₂₀₁ to R₂₀₃ is an aryl group,namely a compound having an arylsulfonium as its cation.

In such an arylsulfonium compound, all of R₂₀₁ to R₂₀₃ may be arylgroups, or one or two of R₂₀₁ to R₂₀₃ may be aryl groups and theremainder may be an alkyl group or a cycloalkyl group.

Examples of such an arylsulfonium compound include a triarylsulfoniumcompound, a diarylalkylsulfonium compound, an aryldialkylsulfoniumcompound, a diarylcycloalkylsulfonium compound and anaryldicycloalkylsulfonium compound.

The aryl group in the arylsulfonium compound is preferably an aryl groupsuch as a phenyl group or a naphthyl group, or a hetroaryl group such asan indole residue or a pyrrole residue, far preferably a phenyl group oran indole residue. When the arylsulfonium compound has two or more arylgroups, the two or more aryl groups may be the same or different.

One or two alkyl groups which the arylsulfonium compound has as requiredare preferably 1-15C linear or branched alkyl groups, with examplesincluding a methyl group, an ethyl group, a propyl group, an n-butylgroup, a sec-butyl group and a t-butyl group.

One or two cycloalkyl groups which the arylsulfonium compound has asrequired are preferably 3-15C cycloalkyl groups, with examples includinga cyclopropyl group, a cyclobutyl group and a cyclohexyl group.

The aryl group, the alkyl group or the cycloalkyl group represented byany of R₂₀₁ to R₂₀₃ may have as a substituent an alkyl group(containing, e.g., 1 to 15 carbon atoms), a cycloalkyl group(containing, e.g., 3 to 15 carbon atoms), an aryl group (containing,e.g., 6 to 14 carbon atoms), an alkoxy group (containing, e.g., 1 to 15carbon atoms), a halogen atom, a hydroxyl group or a phenylthio group.Suitable examples of such substituents include 1-12C linear or branchedalkyl groups, 3-12C cycloalkyl groups and 1-12C linear, branched orcyclic alkoxy groups. Of these substituents, 1-4C alkyl groups and 1-4Calkoxy groups are preferred over the others. One of R₂₀₁ to R₂₀₃ mayhave such a substituent, or all of R₂₀₁ to R₂₀₃ may have suchsubstituents. When R₂₀₁ to R₂₀₃ are aryl groups, it is preferable thatsuch a substituent is situated in the p-position of each aryl group.

Next, the compound (ZI-2) is explained below.

The compound (ZI-2) is a compound represented by the formula (ZI) inwhich R₂₀₁ to R₂₀₃ each independently represent an organic group havingno aromatic ring. The term “aromatic ring” as used herein is intended toalso include aromatic rings containing hetero atoms.

The number of carbon atoms in an aromatic ring-free organic group aseach of R₂₀, to R₂₀₃ is generally from 1 to 30, preferably from 1 to 20.

Each of R₂₀₁ to R₂₀₃ is preferably an alkyl group, a cycloalkyl group,an allyl group or a vinyl group, far preferably a linear, branched orcyclic 2-oxoalkyl group, or an alkoxycarbonylmethyl group, particularlypreferably a linear or branched 2-oxoalkyl group.

The alkyl group as each of R₂₀₁ to R₂₀₃ may have either a linear orbranched form, and it is preferably a 1-10C linear or branched group,with examples including a methyl group, an ethyl group, a propyl group,a butyl group and a pentyl group. The alkyl group as each of R₂₀₁ toR₂₀₃ is far preferably a linear or branched 2-oxoalkyl group, or analkoxycarbonylmethyl group.

The cycloalkyl group as each of R₂₀₁ to R₂₀₃ is preferably a 3-10Ccycloalkyl group, such as a cyclopentyl group, a cyclohexyl group or anorbornyl group. The cycloalkyl group as each of R₂₀₁ to R₂₀₃ is farpreferably a cyclic 2-oxoalkyl group.

Suitable examples of a linear, branched or cyclic 2-oxoalkyl group aseach of R₂₀₁ to R₂₀₃ include the above-recited alkyl and cycloalkylgroups having >C═O at their respective 2-positions.

The alkoxy moiety in an alkoxycarbonylmethyl group as each of R₂₀₁ toR₂₀₃ is preferably a 1-5C alkoxy group (such as a methoxy, ethoxy,propoxy, butoxy or pentoxy group).

Each of groups represented by R₂₀₁ to R₂₀₃ may further be substitutedwith a halogen atom, an alkoxy group (containing, e.g., 1 to 5 carbonatoms), a hydroxyl group, a cyano group or a nitro group.

The compound (ZI-3) is a compound represented by the following formula(ZI-3), namely a compound having a phenacylsulfonium salt structure.

In the formula (ZI-3), R_(1c) to R_(5c) each represent a hydrogen atom,an alkyl group, a cycloalkyl group, an alkoxy group or a halogen atomindependently.

R_(6c) and R_(7c) each represent a hydrogen atom, an alkyl group or acycloalkyl group independently.

R_(x) and R_(y) each represent an alkyl group, a cycloalkyl group, anallyl group or a vinyl group independently.

Any two or more of R_(1c) to R_(7c) may combine with one another to forma ring structure, and R_(x) and R_(y) may also combine with each otherto form a ring structure. In such a ring structure, an oxygen atom, asulfur atom, an ester linkage or an amide linkage may be contained. Thegroup formed by combining any two or more of R_(1c) to R_(7c) or bycombining R_(x) and R_(y) may be a butylene group or a pentylene group.

X⁻ represents a non-nucleophilic anion, and examples thereof include thesame non-nucleophilic anions as examples of X⁻ in formula (ZI).

The alkyl group as each of R_(1c) to R_(7c) may have either a linearform or a branched form, and suitable examples thereof include 1-20Clinear and branched alkyl groups, preferably 1-12C linear and branchedalkyl groups, such as a methyl group, an ethyl group, a linear orbranched propyl group, linear or branched butyl groups, and linear orbranched pentyl groups.

Suitable examples of the cycloalkyl group as each of R_(1c) to R_(7c)include 3-8C cycloalkyl groups, such as a cyclopentyl group and acyclohexyl group.

The alkoxy group as each of R_(1c) to R_(5s) may have either a linearform, or a branched form, or a cyclic form, and examples thereof include1-10C alkoxy groups, preferably 1-5C linear and branched alkoxy groups(such as a methoxy group, an ethoxy group, a linear or branched propoxygroup, linear or branched butoxy groups, and linear or branched pentoxygroups) and 3-8C cycloalkoxy groups (such as a cyclopentyloxy group anda cyclohexyloxy group).

It is preferable that any of R_(1c) to R_(5r) is a linear or branchedalkyl group, a cycloalkyl group, or a linear, branched or cyclic alkoxygroup, and it is far preferable that the number of total carbon atoms inR_(1c) to R_(5c) is from 2 to 15. By respond to this request, thesolvent solubility can be enhanced, and development of particles duringstorage can be inhibited.

Examples of the alkyl group as each of R_(x) and R_(y) include the samegroups as examples of the alkyl group as each of R_(1c) to R_(7c),preferably linear and branched 2-oxoakyl groups and alkoxycarbonylmethylgroups.

Examples of the cycloalkyl group as each of R_(x) and R_(y) include thesame groups as examples of the cycloalkyl group as each of R_(1c) toR_(7c), preferably cyclic 2-oxoakyl groups

Examples of the linear, branched and cyclic 2-oxoalkyl groups includethe same alkyl and cycloalkyl groups as R_(1c) to R_(7c) may represent,except that they have >C═O at their respective 2-positions.

The alkoxy moiety in the alkoxycarbonylmethyl group includes the samealkoxy groups as R_(1c) to R_(5c) each may represent.

Each of R_(x) and R_(y) is preferably an alkyl group containing at least4 carbon atoms, far preferably an alkyl group containing at least 6carbon atoms, further preferably an alkyl group containing at least 8carbon atoms.

In the formulae (ZII) and (ZIII) each, R₂₀₄ to R₂₀₇ each represent anaryl group, an alkyl group or a cycloalkyl group independently.

The aryl group as each of R₂₀₄ to R₂₀₇ is preferably a phenyl group or anaphthyl group, far preferably a phenyl group.

The alkyl group as each of R₂₀₄ to R₂₀₇ may have either a linear form ora branched form, with suitable examples including 1-10C linear andbranched alkyl groups, such as a methyl group, an ethyl group, a propylgroup, a butyl group and a pentyl group.

The cycloalkyl group as each of R₂₀₄ to R₂₀₇ is preferably a 3-10Ccycloalkyl group, with examples including a cyclopentyl group, acyclohexyl group and a norbornyl group.

The alkyl, cycloalkyl and aryl groups which R₂₀₄ to R₂₀₇ each canrepresent may have substituents. Examples of such substituents includean alkyl group (containing, e.g., 1 to 15 carbon atoms), a cycloalkylgroup (containing, e.g., 3 to 15 carbon atoms), an aryl group(containing, e.g., 6 to 15 carbon atoms), an alkoxy group (containing,e.g., 1 to 15 carbon atoms), a halogen atom, a hydroxyl group and aphenylthio group.

X⁻ represents a non-nucleophilic anion, and examples thereof include thesame non-nucleophilic anions as the X⁻ in the formula (ZI) represents.

As examples of a compound which can generate an acid upon irradiationwith an actinic ray or radiation and is usable in the invention,compounds represented by the following formulae (ZIV), (ZV) and (ZVI)can further be given.

In the formulae (ZIV) to (ZVI), Ar₃ and Ar₄ each represent an aryl groupindependently.

R₂₀₆ represents an alkyl group, a cycloalkyl group or an aryl group.

R₂₀₇ and R₂₀₈ each represent an alkyl group, a cycloalkyl group, an arylgroup or an electron-attracting group. R₂₀₇ is preferably an aryl group.R₂₀₈ is preferably an electron-attracting group, far preferably a cyanogroup or a fluoroalkyl group.

A represents an alkylene group, an alkenylene group or an arylene group.

Of the compounds that can decompose upon irradiation with an actinic rayor radiation to generate acids, the compounds represented by (ZI) to(ZIII) are preferred over the others.

Examples of particularly preferred ones of compounds capable ofdecomposing upon irradiation with an actinic ray or radiation togenerate acids are illustrated below.

Acid generators can be used singly or as combinations of two or morethereof. When two or more types of acid generators are used incombination, it is preferred to combine compounds generating two typesof organic acids differing from each other by at least two in the totalnumber of atoms, except for hydrogen atoms.

The content of acid generators in a positive resist composition ispreferably from 0.1 to 20 mass %, far preferably from 0.5 to 10 mass %,further preferably from 1 to 7 mass %, based on the total solids in thecomposition.

[3] Silicon-Containing Resin (C)

The positive resist composition according to the invention ischaracterized by incorporation of a silicon-containing resin having atleast one group selected from the following category (X), (XI) or (XII)(which is also referred to as “a resin of Component (C)” or “asilicon-containing Resin (C)”).

(X): Alkali-soluble groups.

(XI): Groups capable of decomposing under action of an alkalinedeveloper and increasing solubility of a resin of Component (C) in thealkaline developer (hereinafter referred to as “alkali-hydrolyzablegroups”, too).

(XII): Groups capable of decomposing under action of an acid andincreasing solubility of a resin of Component (C) in an alkalinedeveloper (hereinafter referred to as “acid-decomposable groups”, too).

(X) Alkali-Soluble Group

The term “alkali-soluble group” as used herein refers to the group bythe presence of which the silicon-containing Resin (C) can increase itssolubility in a 2.38 mass % aqueous solution of tetramethylammoniumhydroxide at 23° C. when compared with the case where the alkali-solublegroup (X) is absent therein, and the alkali-soluble group is preferablyan acidic group having a pKa of 0.0 to 15.0, especially 3.0 to 12.0.

Suitable examples of an alkali-soluble group (X) include groups having aphenolic hydroxyl group, a carboxylic group, a fluorinated alcoholgroup, a sulfonic acid group, a sulfonamide group, a sulfonylimidegroup, an (alkylsulfonyl)(alkylcarbonyl)methylene group, an(alkylsulfonyl)(alkylcarbonyl)imide group, a bis(alkylcarbonyl)methylenegroup, a bis(alkylcarbonyl)imide group, a bis(alkylsulfonyl)methylenegroup, a bis(alkylsulfonyl)imide group, a tris(alkylcarbonyl)methylenegroup and a tris(alkylsulfonyl)methylene group.

Of these alkali-soluble groups, a fluorinated alcohol group (preferablya hexafluoroisopropanol group, or —C(CF₃)(CF₃)(OH)) and a sulfonylimidegroup are preferred over the others.

(XI) Group Capable of Decomposing Under Action of Alkaline Developer andIncreasing Solubility of Resin of Component (C) in Alkaline Developer

The term “group capable of decomposing under action of an alkalinedeveloper and increasing solubility of a resin of Component (C) in thealkaline developer” refers to the group undergoing hydrolysis reactionin an alkaline developer and being converted into an alkali-solublegroup (X).

Suitable examples of an alkali-hydrolyzable group include a lactonegroup, an ester group, a sulfonamide group, an acid anhydride group andan acid imide group, preferably a lactone group, a sulfonamide group andacid imide group.

(XII) Group Capable of Decomposing Under Action of Acid and IncreasingSolubility of Resin of Component (C) in Alkaline Developer

The term “group capable of decomposing under action of an acid andincreasing solubility of a resin of Component (C) in an alkalinedeveloper refers to the group undergoing decomposition reaction bycatalysis of an acid generated in exposed areas at the step of heatingafter exposure (or the step usually referred to as “Post Exposure Bake(=PEB)”) as included in a general resist pattern forming process andbeing converted into an alkali-soluble group (X).

Examples of such an acid-decomposable group include the sameacid-decomposable groups as recited in the description of the resin ofComponent (A).

When the silicon-containing Resin (C) has either an alkali-soluble group(X), or an alkali-hydrolyzable group (XI), or both, it is preferablethat no acid-decomposable group (XII) is contained therein.

When the silicon-containing Resin (C) has an acid-decomposable group(XII), on the other hand, it is preferable that neither alkali-solublegroup (X) nor alkali-hydrolyzable group (XI) is contained therein.

The silicon-containing Resin (C) may also be a resin having at least onegroup selected from the categories (X) to (XII) and being soluble inalkali and/or increasing its solubility in an alkaline developer underaction of an acid.

The wording “soluble in alkali” for the silicon-containing Resin (C)means that the resin is soluble in an alkaline developer as mentionedbelow (usually an alkaline aqueous solution having a pH of 10.0 to 15.0at 23° C.).

When the silicon-containing Resin (C) is a resin soluble in alkali, ithas an alkali-soluble group (X) and/or a group (XI) that can behydrolyzed by an alkaline developer and made soluble. Examples of groups(X) and (XI) include the same alkali-soluble groups andalkali-hydrolyzable groups as recited above.

The wording “acid-decomposable” for the silicon-containing Resin (C)means that the resin can increase its solubility in an alkalinedeveloper by the action of an acid.

When the silicon-containing Resin (C) is a resin whose solubility in analkaline developer can be increased by the action of an acid, it has agroup (XII) capable of generating an alkali-soluble group throughdecomposition under action of an acid (acid-decomposable group), or aprotected alkali-soluble group. Examples of such a group include thesame acid-decomposable groups as the resin of Component (A) has.

When the silicon-containing Resin (C) is soluble in alkali, the Resin(C) is preferably an alkali-soluble resin causing no increase inalkaline developer solubility under action of an acid.

When the silicon-containing Resin (C) is a resin capable of increasingits solubility in an alkaline developer under action of acid, it ispreferable that the solubility in an alkaline developer is increased bythe action of an acid and the unexposed areas are insoluble in alkali.

Silicon atoms of the silicon-containing Resin (C) may be contained inrepeating units having either alkali-soluble groups (X), oralkali-hydrolyzable groups (XI), or acid-decomposable groups (XII), orrepeating units other than those having groups (X) to (XII).

Specifically, it is preferable that a silicon atom or silicon atoms arecontained in either a repeating unit represented by the followingformula (C1), or a repeating unit represented by the following formula(C2).

In the formulae (C1) and (C2), X₁₁ represents an oxygen atom or—N(R₁₃)—. R₁₃ represents a hydrogen atom, an alkyl group or a cycloalkylgroup. The alkyl group may be linear or branched, and may have asubstituent, such as a halogen atom.

R₁₁ represents a hydrogen atom, a halogen atom, an alkyl group or acycloalkyl group. The alkyl group may be linear or branched, and mayhave a substituent, such as a halogen atom.

R₁₂ and R₂₁ each represent an organic group having at least one siliconatom.

The alkyl groups of R₁₁ and R₁₃ are preferably 1-5C alkyl groups, withexamples including a methyl group, an ethyl group and a t-butyl group.

The cycloalkyl groups of R₁₁ and R₁₃ are preferably 3-10C cycloalkylgroups, with examples including a cyclohexyl group and a cyclooctylgroup.

Examples of repeating units having silicon atoms in thesilicon-containing Resin (C) are illustrated below, but these examplesshould not be construed as limiting the scope of the invention.

The silicon-containing Resin (C) in the positive resist compositionaccording to the invention may further contain fluorine atoms.

When the silicon-containing Resin (C) contains fluorine atoms, it ispreferable that the fluorine atoms are contained in the form of groupsselected from the following categories (F-a) to (F-c).

(F-a): Alkyl groups having fluorine atoms

(F-b): Cycloalkyl groups having fluorine atoms

(F-c): Aryl groups having fluorine atoms

The alkyl groups falling under (F-a) are preferably 1-4C linear orbranched alkyl groups which are each substituted with at least onefluorine atom, and they may further have other substituents.

The cycloalkyl groups falling under (F-b) are preferably mononuclear orpolynuclear cycloalkyl groups which are each substituted with at leastone fluorine atom, and they may further have other substituents.

The aryl groups falling under (F-c) are preferably aryl groups, such asa phenyl group and a naphthyl group, which are each substituted with atleast one fluorine atom, and they may further have other substituents.

When the silicon-containing Resin (C) has fluorine atoms, the fluorineatoms may be present in either the main chain or side chains, but theyare preferably present in side chains.

When the silicon-containing Resin (C) has fluorine atoms, thealkali-soluble groups (X), alkali-decomposable groups (XI) or/andacid-decomposable groups (XII) contained in the silicon-containing Resin(C) can include fluorine-containing ones. For instance, thesilicon-containing Resin (C) can contain a fluorinated alcohol grouplike a hexafluoroisopropanol group as an alkali-soluble group (X).

When the silicon-containing Resin (C) has fluorine atoms, the fluorineatoms may be present, as mentioned above, in repeating units havingalkali-soluble groups (X), alkali-hydrolyzable groups (XI) oracid-decomposable groups (XII) in conjunction with such groups, or inrepeating units other than those having groups (X) to (XII).

More specifically, it is preferable that fluorine atoms are present inthe form of either repeating units represented by the following formula(C3) or repeating units represented by the following formula (C4).

In the formulae (C3) and (C4), X₃₁ represents an oxygen atom or—N(R₃₃)—. R₃₃ represents a hydrogen atom, an alkyl group or a cycloalkylgroup. The alkyl group may be linear or branched, and may have asubstituent, such as a halogen atom.

R₃₁ represents a hydrogen atom, a halogen atom, an alkyl group or acycloalkyl group. The alkyl group may be linear or branched, and mayhave a substituent, such as a halogen atom.

R₃₂ and R₄₁ each represent an organic group having at least one fluorineatom.

The alkyl group which R₃₁ and R₃₃ each can represent is preferably a1-5C alkyl group, such as a methyl group, an ethyl group or a t-butylgroup.

The cycloalkyl group which R₃₁ and R₃₃ each can present is preferably a3-10C cycloalkyl group, such as a cyclohexyl group or a cyclooctylgroup.

Examples of a fluorine-containing repeating unit in cases where thesilicon-containing Resin (C) has fluorine atoms are illustrated below,but these examples should not be construed as limiting the scope of theinvention.

Examples of the silicon-containing Resin (C) are illustrated below, butthese examples should not be construed as limiting the scope of theinvention.

When the silicon-containing resin (C) is a resin having alkali-solublegroups (X) and/or alkali-decomposable groups (XI), the amount ofalkali-soluble groups (X) (acid groups) and/or alkali-decomposablegroups (XI) (acid groups produced by alkali hydrolysis) is preferablyfrom 2 to 10 milliequivalent/g, far preferably from 2 to 8milliequivalent/g, in terms of the acid value of the silicon-containingResin (C). The acid value of a compound is determined by measurement ofthe amount (mg) of potassium hydroxide required for neutralizing thecompound.

When the silicon-containing Resin (C) contains acid-decomposable groups(XII), the content of acid-decomposable groups is preferably from 5 to100 mole %, far preferably from 10 to 100 mole %, in terms of theproportion by mole % of the repeating units having the acid-decomposablegroups.

The silicon-containing Resin (C) contains silicon atoms in a proportionof preferably 2 to 50 mass %, far preferably 2 to 30 mass %, based onthe molecular weight of Resin (C). In addition, it is preferable thatthe silicon-containing repeating units make up 10 to 100 mass %,especially 20 to 100 mass %, of the silicon-containing Resin (C).

The weight-average molecular weight of the silicon-containing Resin (C)is preferably from 1,000 to 100,000, far preferably from 1,000 to50,000.

The content of residual monomers in the silicon-containing Resin (C) ispreferably from 0 to 10 mass %, far preferably from 0 to 5 mass %.Further, it is preferable to use the silicon-containing Resin (C) havinga molecular weight distribution (Mw/Mn, also referred to as thedispersion degree) in the range of 1 to 5, especially 1 to 3, from theviewpoints of resolution, resist profile, sidewall of resist patternsand roughness.

The amount of silicon-containing Resin (C) added to a positive resistcomposition is preferably from 0.1 to 30 mass %, far preferably from 0.1to 10 mass %, further preferably from 0.1 to 5 mass %, based on thetotal solids in the positive resist composition.

As the silicon-containing Resin (C), the silicon-containing resins asrecited above may be used alone or as a mixture of two or more thereof.

As with the case of the resin of Component (A), it is natural for thesilicon-containing Resin (C) to be reduced in impurities includingmetals, and besides, it is preferable that the content of residualmonomers and oligomer components in the Resin (C) is below a specifiedvalue, e.g., below 0.1 mass % in HPLC terms. By meeting theserequirements, the silicon-containing Resin (C) can contribute to notonly improvements in resist sensitivity, resolution, process stabilityand pattern profile but also realization of a resist compositionsuperior in point of reduction in submerged extraneous matter andsensitivity change with the passage of time.

As to the silicon-containing Resin (C), various commercial products canbe utilized, and silicon-containing resins for Component (C) can besynthesized in usual ways. For instance, silicon-containing resins forComponent (C) can be obtained by radical polymerization and generalpurification as in the case of the resin of Component (A).

[4] Solvent (D)

Examples of a solvent which can be used in dissolving each ingredienttherein to prepare a positive resist composition include organicsolvents, such as an alkylene glycol monoalkyl ether carboxylate, analkylene glycol monoalkyl ether, an alkyl lactate, an alkylalkoxypropionate, a 4-10C cyclic lactone, a 4-10C monoketone compoundwhich may contain a ring, an alkylene carbonate, an alkyl alkoxyacetateand an alkyl pyruvate.

Suitable examples of an alkylene glycol monoalkyl ether carbonateinclude propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, propylene glycol monopropyl ether acetate,propylene glycol monobutyl ether acetate, propylene glycol monomethylether propionate, propylene glycol monoethyl ether propionate, ethyleneglycol monomethyl ether acetate, and ethylene glycol monoethyl etheracetate.

Suitable examples of an alkylene glycol monoalkyl ether includepropylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monopropyl ether, propylene glycol monobutyl ether,ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether.

Suitable examples of an alkyl lactate include methyl lactate, ethyllactate, propyl lactate, and butyl lactate.

Suitable examples of an alkyl alkoxypropionate include ethyl3-ethoxypropionate, methyl 3-methoxypropionate, methyl3-ethoxypropionate, and ethyl 3-methoxypropionate.

Suitable examples of a 4-10C cyclic lactone include β-propiolactone,β-butyrolactone, γ-butyrolactone, α-methyl-γ-butyrolactone,β-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-octanoiclactone, and α-hydroxy-γ-butyrolactone.

Suitable examples of a 4-10C monoketone compound which may contain aring include 2-butanone, 3-methylbutanone, pinacolone, 2-pentanone,3-pentanone, 3-methyl-2-pentanone, 4-methyl-2-pentanone,2-methyl-3-pentanone, 4,4-dimethyl-2-pentanone,2,4-dimethyl-3-pentanone, 2,2,4,4-tetramethyl-3-pentanone, 2-hexanone,3-hexanone, 5-methyl-3-hexanone, 2-heptanone, 3-heptanone, 4-heptanone,2-methyl-3-heptanone, 5-methyl-3-heptanone, 2,6-dimethyl-4-heptanone,2-octanone, 3-octanone, 2-nonanone, 3-nonanone, 5-nonanone, 2-decanone,3-decanone, 4-decanone, 5-hexene-2-one, 3-pentene-2-one, cyclopentanone,2-methylcyclopentanone, 3-methylcyclopentanone,2,2-dimethylcyclopentanone, 2,4,4-trimethylcyclopentanone,cyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone,4-ethylcyclohexanone, 2,2-dimethylcyclohexanone,2,6-dimethylcyclohexanone, 2,2,6-trimethylcyclohexanone, cycloheptanone,2-methylcycloheptanone, and 3-methylcycloheptanone.

Suitable examples of an alkylene carbonate include propylene carbonate,vinylene carbonate, ethylene carbonate, and butylene carbonate.

Suitable examples of an alkyl alkoxyacetate includeacetate-2-methoxyethyl, acetate-2-ethoxyethyl,acetate-2-(2-ethoxyethoxy)ethyl, acetate-3-methoxy-3-methylbutyl, andacetate-1-methoxy-2-propyl.

Suitable examples of an alkyl pyruvate include methyl pyruvate, ethylpyruvate, and propyl pyruvate.

Solvents used to advantage include solvents having boiling points of130° C. or above at ordinary temperatures and under normal atmosphericpressure. Examples of such solvents include cyclopentanone,γ-butyrolactone, cyclohexanone, ethyl lactate, ethylene glycol monoethylether acetate, propylene glycol monomethyl ether acetate, ethyl3-ethoxypropionate, ethyl pyruvate, acetate-2-ethoxyethyl,acetate-2-(2-ethoxyethoxy)ethyl, and propylene carbonate.

In the invention, the solvents recited above may be used alone, or ascombinations of two or more thereof.

The solvent used in the invention may also be a mixture of a solventhaving a hydroxyl group in its structure and a solvent having nohydroxyl group.

Examples of a solvent having a hydroxyl group include ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,propylene glycol, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, and ethyl lactate. Of these solvents, propylene glycolmonomethyl ether and ethyl lactate are preferred over the others.

Examples of a solvent having no hydroxyl group include propylene glycolmonomethyl ether acetate, ethyl ethoxypropionate, 2-heptanone,γ-butyrolactone, cyclohexanone, butyl acetate, N-methylpyrrolidone,N,N-dimethylacetamide, and dimethyl sulfoxide. Of these solvents,propylene glycol monomethyl ether acetate, ethyl ethoxypropionate,2-heptanone, γ-butyrolactone, cyclohexanone and butyl acetate arepreferred over the others. Further, propylene glycol monomethyl etheracetate, ethyl ethoxypropionate and 2-heptanone in particular are usedto advantage.

The mixing ratio (by mass) between the solvent containing a hydroxylgroup and the solvent containing no hydroxyl group is from 1/99 to 99/1,preferably from 10/90 to 90/10, far preferably from 20/80 to 60/40. Amixed solvent containing a solvent having no hydroxyl group in aproportion of 50 weight % or above is particularly preferred from theviewpoint of coating evenness.

[5] (E): Basic Compound

For the purpose of reducing performance changes with the passage of timefrom exposure to heating, it is preferable that a basic compound iscontained in the positive resist composition according to the invention.

Examples of such a basic compound include compounds having the followingstructures (A) to (E).

In the formula (A), R²⁰⁰, R²⁰¹ and R²⁰², which may be the same ordifferent, each represent a hydrogen atom, a 1-20C alkyl group, a 3-20Ccycloalkyl group or a 6-20C aryl group independently. Herein, R²⁰⁰ andR²⁰¹ may combine with each other to form a ring. The alkyl group may bean unsubstituted one, or may have a substituent. Suitable examples of analkyl group having a substituent include 1-20C aminoalkyl groups, 1-20Chydroxyalkyl groups and 1-20C cyanoalkyl groups.

In the formula (E), R²⁰³, R²⁰⁴, R²⁰⁵, and R²⁰⁶, which may be the same ordifferent, each represent a 1-20C alkyl group.

The alkyl groups in the formulae (A) and (E) are preferablyunsubstituted alkyl groups.

Examples of such basic compounds include substituted or unsubstitutedprimary, secondary and tertiary aliphatic amines, aromatic amines,heterocyclic amines, amide derivatives, imide derivatives, andnitrogen-containing compounds having cyano groups. Of these compounds,aliphatic amines, aromatic amines and heterocyclic amines are preferredover the others. Suitable examples of substituents which those compoundsmay have include amino groups, alkyl groups, alkoxy groups, acyl groups,acyloxy groups, aryl groups, aryloxy groups, a nitro group, a cyanogroup, ester groups and lactone groups.

Examples of favorable compounds include guanidine, aminopyrrolidine,pyrazole, pyrazoline, piperazine, aminomorpholine, aminoalkylmorpholinesand piperidine, which each may have a substituent. Examples of morefavorable compounds include compounds having an imidazole structure, adiazabicyclo structure, an onium hydroxide structure, an oniumcarboxylate structure, a trialkylamine structure, an aniline structureand a pyridine structure, respectively, an alkylamine derivative havinga hydroxyl group and/or an ether linkage, and an aniline derivativehaving a hydroxyl group and/or an ether linkage.

Examples of the compound having an imidazole structure includeimidazole, 2,4,5-triphenylmidazole and benzimidazole. Examples of thecompound having a diazabicyclo structure include1,4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]nona-5-ene and1,8-diazabicyclo[5.4.0]undeca-7-ene. Examples of the compound having anonium hydroxide structure include triarylsulfonium hydroxides,phenacylsulfonium hydroxides and sulfonium hydroxides having 2-oxoalkylgroups, and more specifically, include triphenylsulfonium hydroxide,tris(t-butylphenyl)sulfonium hydroxide, bis(t-butylphenyl)iodoniumhydroxide, phenacylthiophenium hydroxide and 2-oxopropylthiopheniumhydroxide. The compound having an onium carboxylate structure is acompound having the structure corresponding to the substitution ofcarboxylate for the anion moiety of the compound having an oniumhydroxide structure, with examples including acetate,adamantane-1-carboxylate and perfluoroalkylcarboxylates. Examples of thecompound having a trialkylamine structure include tri(n-butyl)amine andtri(n-octyl)amine. Examples of the aniline compounds include2,6-diisopropylaniline and N,N-dimethylaniline. Examples of thealkylamine derivative having a hydroxyl group and/or an ether linkageinclude ethanolamine, diethanolamine, triethanolamine andtris(methoxyethoxyethyl)amine. As an example of the aniline derivativehaving a hydroxyl group and/or an ether linkage,N,N-bis(hydroxyethyl)aniline can be given.

These basic compounds are used alone or as combinations of two or morethereof.

The amount of basic compound or compounds used is generally from 0.001to 10 mass %, preferably 0.01 to 5 mass %, based on the total solids inthe positive resist composition.

As to the usage ratio of acid generator(s) to basic compound(s) in thecomposition, the acid generator/basic compound ratio (by mole)=2.5 to300 is suitable. More specifically, it is appropriate that the ratio bymole be adjusted to at least 2.5 in point of sensitivity and resolution,while it be adjusted to at most 300 from the viewpoint of preventing theresolution from decreasing by thickening of resist patterns with thepassage of time from the end of exposure to heating treatment. The acidgenerator/basic compound ratio (by mole) is preferably from 5.0 to 200,far preferably from 7.0 to 150.

[6] (F): Surfactant

It is preferable that the positive resist composition according to theinvention further contains a surfactant, specifically a surfactantcontaining at least one fluorine atom and/or at least one silicon atom(namely either a surfactant containing at least one fluorine atom, or asurfactant containing at least one silicon atom, or a surfactantcontaining both fluorine and silicon atoms), or a combination of atleast two of these surfactants.

Incorporation of such a surfactant in the positive resist compositionaccording to the invention makes it possible to provide resist patternshaving strong adhesion and reduced development defect while ensuring thecomposition both satisfactory sensitivity and high resolution in thecase of using an exposure light source of 250 nm or below, especially220 nm or below.

Examples of a surfactant containing at least one fluorine atom and/or atleast one silicon atom include the surfactants disclosed inJP-A-62-36663, JP-A-61-226746, JP-A-61-226745, JP-A-62-170950,JP-A-63-34540, JP-A-7-230165, JP-A-8-62834, JP-A-9-54432, JP-A-9-5988,JP-A-2002-277862, and U.S. Pat. Nos. 5,405,720, 5,360,692, 5,529,881,5,296,330, 5,436,098, 5,576,143, 5,294,511 and 5,824,451. In addition,the following commercially available surfactants can be used as theyare.

Examples of commercial surfactants which can be used include fluorine-or silicon-containing surfactants, such as EFTOP EF301 and EF303(produced by Shin-Akita Kasei K. K.), Florad FC430, 431 and 4430(produced by Sumitomo 3M, Inc.), Megafac F171, F173, F176, F189, F113,F110, F177, F120 and R⁰⁸ (produced by Dainippon Ink & Chemicals, Inc.),Surflon S-382, SC101, 102, 103, 104, 105 and 106 (produced by AsahiGlass Co., Ltd.), Troysol S-366 (produced by Troy Chemical Industries,Inc.), GF-300 and GF-150 (produced by Toagosei Co., Ltd.), Surflon S-393(produced by Seimi Chemical Co., Ltd.), EFTOP EF121, EF122A, EF122B,RF122C, EF125M, EF135M, EF351, EF352, EF801, EF802 and EF601 (producedby JEMCO Inc.), PF636, PF656, PF6320 and PF6520 (produced by OMNOVASolutions Inc.), and FTX-204D, 208G, 218G, 230G, 208D, 212D, 218D and222D (produced by NEOS). Moreover, organosiloxane polymer KP-341(produced by Shin-Etsu Chemical Co., Ltd.) can be used as asilicon-containing surfactant.

In addition to known surfactants as recited above, the surfactantsusable in the invention include surfactants using polymers containingfluorinated aliphatic groups derived from fluorinated aliphaticcompounds synthesized by a telomerization method (also referred to as atelomer method) or an oligomerization method (also referred to as anoligomer method). These fluorinated aliphatic compounds can besynthesized according to the methods disclosed in JP-A-2002-90991.

The polymers containing fluorinated aliphatic groups are preferablycopolymers of fluorinated aliphatic group-containing monomers andpoly(oxyalkylene) acrylates and/or poly(oxyalkylene) methacrylates,wherein the fluorinated aliphatic group-containing units may bedistributed randomly or in blocks. Examples of such poly(oxyalkylene)groups include a poly(oxyethylene) group, a poly(oxypropylene) group anda poly(oxybutylene) group. In addition, the poly(oxyalkylene) groups maybe units containing alkylene groups of different chain lengths in theirrespective oxyalkylene chains, such as poly(oxyethyleneblock-oxypropylene block-oxyethylene block combination) andpoly(oxyethylene block-oxypropylene block combination). Further, thecopolymers of fluorinated aliphatic group-containing monomers andpoly(oxyalkylene) acrylates (or methacrylates) may be binary copolymersor at least ternary copolymers prepared by copolymerizing at least twodifferent kinds of fluorinated aliphatic group-containing monomers andat least two different kinds of poly(oxyalkylene) acrylates (ormethacrylates) at the same time.

Examples of commercially available surfactants of such types includeMegafac F178, F-470, F-473, F-475, F-476 and F-472 (produced byDainippon Ink & Chemicals, Inc.). Additional examples of surfactants ofsuch types include a copolymer of C₆F₁₃ group-containing acrylate (ormethacrylate) and poly(oxyalkylene) acrylate (or methacrylate), and acopolymer of C₃F₇ group-containing acrylate (or methacrylate),poly(oxyethylene) acrylate (or methacrylate) and poly(oxypropylene)acrylate (or methacrylate).

Alternatively, it is also possible to use surfactants other thansurfactants containing fluorine and/or silicon atoms. Examples of suchsurfactants include nonionic surfactants, such as polyoxyethylene alkylethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearylether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether),polyoxyethylene alkyl aryl ethers (e.g., polyoxyethylene octyl phenolether, polyoxyethylene nonyl phenol ether),polyoxyethylene-polyoxyproppylene block copolymers, sorbitan fatty acidesters (e.g., sorbitan monolaurate, sorbitan monopalmitate, sorbitanmonostearate, sorbitan monooleate, sorbitan trioleate, sorbitantristearate), and polyoxyethylene sorbitan fatty acid esters (e.g.,polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylenesorbitan trioleate, polyoxyethylene sorbitan tristearate).

These surfactants may be used alone, or as combinations of two or morethereof.

The amount of surfactants used is preferably from 0.01 to 10 mass %,preferably 0.1 to 5 mass %, based on the total ingredients (exclusive ofa solvent) in the positive resist composition.

[7] (G): Onium Carboxylate

The positive resist composition for use in the invention may furthercontain an onium carboxylate. Examples of such an onium carboxylateinclude sulfonium carboxylates, iodonium carboxylates and ammoniumcarboxylates. Of these onium salts, iodonium salts and sulfonium saltsare especially preferred. In addition, it is preferable that neitheraromatic groups nor carbon-carbon double bonds are contained in thecarboxylate residues of onium carboxylates which can be used in theinvention. Examples of an especially suitable anion moiety include 1-30Clinear and branched alkyl carboxylate anions and mononuclear orpolynuclear cycloalkyl carboxylate anions. Of these anions, thecarboxylate anions whose alkyl groups are partially or entirelysubstituted by fluorine atoms are preferred over the others. Inaddition, those alkyl chains may contain oxygen atoms. By containing anonium salt having such a carboxylate anion, the resist composition canensure transparency to light with wavelengths of 220 nm or below, andcan have increased sensitivity and resolution and improved pitchdependency and exposure margin.

Examples of a fluorinated carboxylate anion include fluoroacetate anion,difluoroacetate anion, trifluoroacetate anion, pentafluoropropionateanion, heptafluorobutyrate anion, nanofluoropentanate anion,perfluorododecanate anion, perfluorotridecanate anion,perfluorocyclohexanecarboxylate anion and2,2-bistrifluoromethylpropionate anion.

These onium carboxylates can be synthesized by allowing sulfoniumhydroxide, iodonium hydroxide or ammonium hydroxide and carboxylic acidsto react with silver oxide in an appropriate solvent.

The suitable content of onium carboxylate in a composition is from 0.1to 20 mass %, preferably from 0.5 to 10 mass %, far preferably from 1 to7 mass %, of the total solids in the composition.

Other Additives

The positive resist composition according to the invention can furthercontain, on an as needed basis, dyes, plasticizers, photosensitizers,light absorbents, alkali-soluble resins, dissolution inhibitors andcompounds which can further dissolution in developers (e.g., phenolcompounds having molecular weights of 1,000 or below, alicyclic oraliphatic compounds having carboxyl groups).

Such phenol compounds 1,000 or below in molecular weight can be easilysynthesized by persons skilled in the art when they refer to the methodsas disclosed in JP-A-4-122938, JP-A-2-28531, U.S. Pat. No. 4,916,210 andEuropean Patent No. 219,294.

Examples of alicyclic and aliphatic compounds having carboxyl groupsinclude carboxylic acid derivatives having steroid structures, such ascholic acid, deoxycholic acid and lithocholic acid, adamantanecarboxylicacid derivatives, adamantanedicarboxylic acid, cyclohexanecarboxylicacid and cyclohexanedicarboxylic acid, but not limited to the compoundsrecited above.

[Physical Properties of Positive Resist Composition]

From the viewpoint of improvement in resolution, it is appropriate thatthe positive resist composition according to the invention be used in acoating thickness of 30 to 250 nm, preferably 30 to 200 nm. The coatingthickness in such a range can be attained by imparting just rightviscosity to the positive resist composition through adjustment of thesolids concentration in the composition to a proper range, therebyenhancing coating suitability and film formability.

The concentration of total solids in the positive resist composition isgenerally from 1 to 10 mass %, preferably from 1 to 8 mass %, farpreferably from 1.0 to 7.0 mass %.

[Preparation of Positive Resist Composition]

The positive resist composition according to the invention is preparedby dissolving the ingredients as described above in a specified solvent,preferably the mixed solvent as described above, and passing theresulting solution through a filter. The filter suitably used forfiltration is a polytetrafluoroethylene, polyethylene or nylon filtercapable of filtering to 0.1 microns or below, preferably 0.05 microns orbelow, far preferably 0.03 microns or below.

[Pattern Forming Method]

The pattern forming method of the invention is described below indetail.

As a result of our intensive study of what gives rise to deteriorationin resolution, which is traceable to topple of resist patterns, andsensitivity decrease when a chemical amplification resist is used inimmersion lithography, we have narrowed it down to immersion liquidpermeation into a resist coating which occurs while the resist coatingmaintains contact with the immersion liquid, thereby achieving theinvention.

The image forming method of the invention has steps of:

(i) coating a substrate with the positive resist composition accordingto the invention to form a resist coating,

(ii) exposing the resist coating to light via an immersion liquid,

(iii) removing the immersion liquid remaining on the resist coating,

(iv) heating the resist coating, and

(v) developing the resist coating,

and is distinguished by having the step (iii) of removing the immersionliquid remaining on the resist coating after the step (ii) of exposingthe resist coating to light via the immersion liquid and before the step(iv) of heating the resist coating.

Incidentally, the step (iv) of heating the resist coating is a stepcorresponding to the heating step generally performed after exposure andbefore development for the purpose of promoting conversion ofalkali-insoluble groups in a resist coating to alkali-soluble groups,namely the step referred to as PEB (Post Exposure Bake).

Reaction for converting alkali-insoluble groups in a chemicalamplification resist to alkali-soluble groups occurs at the time of PEBgenerally carried out during or after exposure, so reactions under PEBare important.

Although it was thought that water as the most suitable immersion liquidin the case of using ArF excimer laser is less prone to permeate into aresist coating for ArF excimer laser use because the resist coating isgenerally formed from resin and organic molecules, so it is sufficientlyhydrophobic, we have found that minute quantities of water actuallypermeated into upper part of the resist coating. When the waterpermeates into the resist coating, the resist coating surface and thevicinity of the interface between the resist coating and the substratecome to differ in water content to cause changes in diffusion distanceof a generated acid and rate of conversion reaction fromalkali-insoluble groups into alkali-soluble groups, thereby resulting inunevenness of chemical reaction in the space between the surface and thebottom of the resist coating. Therefore, there is a possibility thatresist patterns of good quality cannot be obtained.

In the case of immersion lithography using exposure wavelengths otherthan the wavelength of ArF, it is also conceivable that minutequantities of immersion liquid will permeate into a resist coating, andthere is a high possibility that resist patterns formed will becomeunsatisfactory.

A feature of the invention consists in that the step (iii) of removingthe immersion liquid remaining on a resist coating is carried out beforePEB, or the step (iv) of heating the resist coating, and therebyreaction for converting alkali-insoluble groups into alkali-solublegroups can be made uniform throughout the coating to result in formationof satisfactory resist patterns.

Examples of a step adoptable as the step (iii) of removing the immersionliquid remaining on a resist coating include (iii-1) a step of removingthe immersion liquid by spinning the substrate, (iii-2) a step ofremoving the immersion liquid by heating the substrate at temperatureson a level that there occurs no conversion from alkali-insoluble groupsinto alkali-soluble groups, and (iii-3) a step of removing the immersionliquid by blowing a gas from a nozzle. These steps can be performed byuse of general apparatus for manufacturing semiconductors, liquidcrystal displays and devices like thermal heads, so they don't requireintroduction of new apparatus and are practical in point of costadvantage. Alternatively, a device permitting hot-air drying may beinstalled in an exposure apparatus or a developing machine, and thedrying may be performed with hot air.

In the step (iii-1) of removing the immersion liquid by spinning asubstrate, the number of revolutions of the substrate is preferably 500rpm or above since the low revs cannot induce a high velocity of airflow on the resist coating surface to result in prolongation of drying.The higher revs the better, because they can make the drying time theshorter and thereby the higher throughput can be attained.

However, the setting of the revs is generally below the upper limitdesignated by the device used. So, for instance, the revs is generallyadjusted to 3,000 rpm or below in the case of spinning a 12-inchcircular silicon-wafer substrate, or 4,000 rpm or below in the case ofspinning an 8-inch circular wafer substrate.

For completion of the drying, it is appropriate that the spinning timeof the substrate be adjusted to 5 seconds or longer, and the longer thebetter. However, in order to minimize throughput penalty, the setting ofthe spinning time may be made with consideration given to the total timeand number of devices required for other steps, such as exposure, PEBand development.

For elimination of the vaporized immersion liquid from apparatus,ventilation of the apparatus is preferred, and the ventilation pressureis preferably 20 Pa or above.

Although the device for spinning a substrate may be any device so longas it has a mechanism for spinning the substrate, the use of developingapparatus, which is general apparatus for manufacturing semiconductors,liquid crystal displays and devices like thermal heads, is advantageousfrom the viewpoint of simplicity in delivery of a substrate fromexposure apparatus to developing apparatus, but the device should not beconstrued as being limited to such apparatus.

In the step (iii-2) of removing the immersion liquid by baking (heating)a resist coating, conversion of alkali-insoluble groups in the resininto alkali-soluble groups during the bake for removal of the immersionliquid allows chemical reaction to occur in a state that the immersionliquid is present in the resist coating, and raises the possibility ofrendering the chemical reaction uneven in the space between the surfaceand bottom of the resist coating. Therefore, it is appropriate that thebake temperature be adjusted to temperatures at which thealkali-insoluble groups in the resin cannot be converted intoalkali-soluble ones.

Further, it is required that the bake temperature be a temperature atwhich no conversion from alkali-insoluble groups into alkali-solublegroups is caused in the resist resin.

As the temperature at which an alkali-insoluble group is converted intoan alkali-soluble group differs depending on the kind of resist,commercially available resists have their recommended post-baketemperatures (namely the foregoing PEB temperatures), and they aregenerally in the range of 90-150° C. At temperatures higher than therecommended temperatures, the conversion reaction from alkali-insolublegroups into alkali-soluble groups occurs with efficiency.

Accordingly, the bake temperature for removal of immersion liquid is atemperature at which alkali-insoluble groups cannot be converted intoalkali-soluble groups, and preferably chosen from the temperatures atleast 20° C. lower than the heating temperature in the step (iv) ofheating the resist coating.

Although the temperature required at the minimum differs depending onthe kind of immersion liquid, there is a high possibility of adoptingwater as an immersion liquid in immersion lithography utilizing ArFexcimer laser and, when water is used as an immersion liquid under thesecircumstances, the heating at a temperature of 40° C. or above ispreferred. However, the immersion liquid should not be construed asbeing limited to water.

Since a short heating time cannot complete the removal of immersionliquid and a long heating time affects throughput, the heating time ispreferably adjusted to the range of 10-120 seconds.

Further, it is preferable that the apparatus is ventilated for thepurpose of eliminating the vaporized immersion liquid from apparatus,and the ventilation pressure is preferably 3 Pa or above. As to thedevice for heating the substrate, although any devices may be used asfar as they have a heating mechanism, it is advantageous to use aheating unit attendant on a developing apparatus as general apparatusfor manufacturing semiconductors, liquid crystal displays and deviceslike thermal heads from the viewpoint of simplicity in delivery of asubstrate from the exposure apparatus to the developing apparatus, butthe device should not be construed as being limited to such unit.

As another example of the step (iii) of removing the immersion liquidremaining on a resist coating, a step of removing the immersion liquidby feeding a water-miscible organic solvent to the resist coatingsurface can be given.

Examples of a water-miscible organic solvent usable therein includealcohol solvents, such as methyl alcohol, ethyl alcohol, n-propylalcohol and isopropyl alcohol. Of these solvents, isopropyl alcohol ispreferred over the others.

A water-miscible organic solvent may be fed onto a wafer surface via adropping nozzle, e.g., under a condition that the wafer is made toadsorb to a holding mount by means of a vacuum chuck. It is preferablethat the solvent feeding is carried out in an amount of 0.1 to 2.0kg/cm² so as to distribute the solvent over the whole surface of thewafer. The solvent feeding may be performed in a state that the waferstands still, or it may be performed as the wafer is rotated at a lowspeed (e.g., 30 rpm). After the solvent feeding is stopped, thewater-miscible organic solvent may be dried by ventilation as the waferis in a stationary state, or by spinning of the wafer at 1,000 rpm orabove.

The amount of immersion liquid remaining in the resist coating aftercompletion of the step (iii) of removing the immersion liquid remainingon the resist coating is preferably 0.1 mass % or below, far preferably0.01 mass % or below.

As a method for measuring a water content in the case of using water ora water solution as the immersion liquid, there is known the method ofscraping the resist coating away from the substrate by use of, e.g., aspatula and measuring its water content with a Karl Fischer MoistureTitrator (MKS-500, made by Kyoto Electronics Manufacturing Co., Ltd.).In the case where the immersion liquid is a non-aqueous solution, on theother hand, there is known the method of dissolving the resist coatingscraped away from the substrate in a solvent, such as cyclohexanone, anddetermining the liquid content by gas chromatography (using, e.g., GC-17Aver. 3, made by Shimadzu Corporation).

In the pattern forming method of the invention, the step (i) of coatinga substrate with a positive resist composition to form a resist coating,the step (ii) of exposing the resist coating via an immersion liquid,the step (iv) of heating the resist coating and the step (v) ofdeveloping the resist coating can be performed using generally knownmethods.

At the removal of the immersion liquid remaining on the resist coating,it is preferable that a liquid film (puddle) of the immersion liquid(preferably purified water) is formed on the resist coating, and thenthe liquid film is removed so as not to left any liquid drops.

The puddle can be formed by making use of the surface tension of theimmersion liquid and putting the immersion liquid on the resist coatingin a condition that the wafer is kept still.

In the invention, it is preferable that the surface of the resistcoating is cleaned prior to the step (ii) of exposing the resist coatingvia the immersion liquid.

The cleaning is performed by bringing a liquid to contact with theresist coating surface and eliminating dirt and particles.

As the liquid brought into contact with the resist coating surface, theimmersion liquid may be used, or a liquid for cleaning, other than theimmersion liquid, may be used.

The heating of the resist coating in the step (iii-2) and the step (iv)is generally carried out by heating the substrate having the resistcoating by means of a hot plate.

After heating the resist coating in the step (iv), the resist coating isgenerally cooled to the vicinity of room temperature (e.g., 23° C.), andthen undergoes development in the step (v).

The invention has no particular restriction as to the wavelength of alight source used in exposure apparatus for immersion lithography, but astart in the study of immersion lithography has been made at thewavelengths of ArF excimer laser (193 nm) and F₂ excimer laser. Theinvention can be applied to immersion lithography at both wavelengths.

The liquid suitable as immersion liquid is transparent to exposurewavelengths, and the refractive index thereof preferably has thesmallest possible temperature coefficient so that the distortion ofoptical images projected onto the resist coating is minimized. In thecase where the exposure light source is ArF excimer laser (wavelength:193 nm) in particular, it is preferable that water is used from theviewpoints of availability and easiness of handling in addition to theaforesaid viewpoints.

When water is used as the immersion liquid, an additive (liquid) capableof reducing the surface tension of water and enhancing the surfaceactivity may be added in a slight proportion. This additive ispreferably a liquid not causing dissolution of the coating layer on thewafer and having a negligibly small effect on an optical coat providedon the underside of lens element.

Suitable examples of such an additive include aliphatic alcoholcompounds having almost the same refractive indexes as that of water,such as methyl alcohol, ethyl alcohol and isopropyl alcohol. Addition ofalcohol having almost the same refractive index as that of water canoffer an advantage that a change in refractive index as the liquid inits entirety can be made minimal even when the alcohol concentration inthe immersion liquid is altered by vaporization of the alcohol.

On the other hand, mixing of a substance opaque to light of 193 nm andimpurities greatly differing in refractive index from water brings aboutdistortion of optical images projected onto the resist, so the waterused is preferably distilled water. Further, purified water havingundergone filtration by passage through an ion exchange filter may beused.

In the invention, the substrate on which the resist coating is formedhas no particular restriction, but it is possible to use any ofinorganic substrates, such as silicon, SiN, or SiO₂/SiN, coating-typeinorganic substrates such as SOG, and substrates generally used in alithography process for manufacturing semiconductors, such as ICs,circuit boards for LCDs and thermal heads, and for photofabrication ofother devices. Further, an organic antireflective film may be formedbetween the resist coating and the substrate, if needed.

Examples of an alkaline developer used in the step of carrying outdevelopment include aqueous alkaline solutions of inorganic alkalis,such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodiumsilicate, sodium metasilicate and aqueous ammonia, primary amines, suchas ethyl amine and n-propylamine, secondary amines, such as diethylamineand di-n-butylamine, tertiary amines, such as triethylamine andmethyldiethylamine, alcohol amines, such as dimethylethanolamine andtriethanolamine, quaternary ammonium salts, such as tetramethylammoniumhydroxide and tetraethylammonium hydroxide, and cyclic amines, such aspyrrole and piperidine.

Further, it is possible to use the alkaline aqueous solution as recitedabove to which an alcohol compound and a surfactant are added inappropriate amounts.

The alkali concentration in an alkaline developer is generally from 0.1to 20 mass %.

The pH of the alkaline developer is generally from 10.0 to 15.0.

As a rinse solution, purified water is used, and thereto an appropriateamount of surfactant may also be added.

After the development-processing or the processing with a rinsesolution, treatment for eliminating the developer or the rinse solutionadhering to patterns by use of a supercritical liquid can further beperformed.

The invention will now be illustrated in greater detail by reference tothe following examples, but these examples should not be construed aslimiting the scope of the invention in any way.

The structures of resins (1) to (26) used as Component (A) in Examplesand Comparative Examples are illustrated below. In addition, thecompositions (which each are expressed in a ratio between proportions(by mole %) of repeating units arranged in the direction from the leftto the right in each individual structural formula), weight-averagemolecular weights (Mw) and dispersion degrees (Mw/Mn) of the resins (1)to (26) are shown in the following Tables 1 and 2.

TABLE 1 Resin Composition Mw Mw/Mn 1 39/20/41 9,800 1.9 2 40/22/3812,000 2.0 3 34/33/33 11,000 2.3 4 45/15/40 10,500 2.1 5 35/15/50 6,7002.2 6 30/25/45 8,400 2.3 7 39/20/41 10,500 2.1 8 49/10/41 9,500 2.5 935/32/33 14,000 2.6 10 35/35/30 6,700 2.3 11 40/22/38 8,500 2.5 1240/20/35/5 12,500 2.4 13 50/50 14,000 1.9 14 40/15/40/5 10,000 1.8 1550/50 8,300 1.5 16 40/15/40/5 9,800 2.3 17 50/50 5,200 2.1 18 35/20/40/56,100 2.3 19 30/30/30/10 8,600 2.5 20 40/20/35/5 12,000 2.1 21 40/20/407,800 1.9 22 80/20 8,800 2.1

TABLE 2 Resin Composition Mw Mw/Mn 23 50/10/40 10,000 1.2 24 40/20/409,600 1.4 25 40/20/30/10 10,400 1.1 26 45/20/30/5 9,900 1.3

SYNTHESIS EXAMPLE 1 Synthesis of Resin (C-1)

(Trimethylsilyl)methyl methacrylate and metacrylic acid were prepared ata ratio of 50 to 50 (by mole), and dissolved in propylene glycolmonomethyl ether acetate, thereby making 450 g of a solution having asolids concentration of 22 mass %. To this solution, a polymerizationinitiator, V-601 produced by Wako Pure Chemical Industries, Ltd., wasadded in a proportion of 5 mole %, and this admixture was added dropwiseto 50 mL of propylene glycol monomethyl ether acetate heated to 80° C.over a 2-hour period in an atmosphere of nitrogen. After conclusion ofthe dropwise addition, the reaction solution was stirred for 2 hours.Thus, a reaction solution (C-1) was obtained. After completion of thereaction, the reaction solution (C-1) was cooled to room temperature,and then poured into a 10-times amount of 90:10 hexane-ethyl acetatemixture to result in precipitation of white powdery matter. This powderymatter was filtered off, thereby collecting the intended resin (C-1)having the structure illustrated hereinafter.

The polymer's compositional ratio (by mole %) determined by ¹³C-NMR andacid value titration was 50/50 (corresponding to the arranging order (inthe direction from the left to the right) of repeating units in thestructural formula, as were the compositional ratios mentioned below).Further, the weight-average molecular weight and dispersion degree ofResin (C-1) were found to be 13,200 and 2.2, respectively, as measuredby GPC and calculated in terms of polystyrene.

SYNTHESIS EXAMPLE 2 Synthesis of Resin (C-2)

Resin (C-2) having the structure illustrated hereinafter was synthesizedin the same manner as the above, except that the ratio between theamounts of monomers prepared was changed to 70/30 (by mole) and thesolvent used for crystallization was changed to methanol. Thecompositional ratio (by mole %) of Resin (C-2) determined by ¹³C-NMR andacid value titration was 32/68. Further, the weight-average molecularweight and dispersion degree of Resin (C-2) were found to be 13,000 and2.1, respectively, as measured by GPC and calculated in terms ofpolystyrene.

SYNTHESIS EXAMPLE 3 Synthesis of Resin (C-3)

Allyltrimethylsilane, maleic anhydride and t-butyl methacrylate wereprepared at a ratio of 40 to 40 to 20 (by mole), and dissolved inpropylene glycol monomethyl ether acetate, thereby making 450 g of asolution having a solids concentration of 50 mass %. To this solution, apolymerization initiator, V-65 produced by Wako Pure ChemicalIndustries, Ltd., was added in a proportion of 4 mole %, and thisadmixture was stirred for 5 hours in an atmosphere of nitrogen. Thus, areaction solution (C-3) was obtained. After completion of the reaction,the reaction solution (C-3) was cooled to room temperature, and thenpoured into a 5-times amount of methanol to result in precipitation ofwhite powdery matter. This powdery matter was filtered off, therebycollecting the intended resin (C-3) having the structure illustratedhereinafter.

The polymer's compositional ratio (by mole %) determined by ¹³C-NMR was35/35/30. Further, the weight-average molecular weight and dispersiondegree of Resin (C-3) were found to be 8,500 and 1.8, respectively, asmeasured by GPC and calculated in terms of polystyrene.

SYNTHESIS EXAMPLE 4 Synthesis of Resin (C-4)

Allyltrimethylsilane, N-ethylmaleimide and metacrylic acid were preparedat a ratio of 35 to 35 to 30 (by mole), and dissolved intetrahydrofuran, thereby making 300 g of a solution having a solidsconcentration of 80 mass %. To this solution, a polymerizationinitiator, V-65 produced by Wako Pure Chemical Industries, Ltd., wasadded in a proportion of 5 mole %, and this admixture was added dropwiseto 30 mL of tetrahydrofuran heated to 65° C. over a 4-hour period in anatmosphere of nitrogen. After conclusion of the dropwise addition, thereaction solution was stirred for 2 hours. Thus, a reaction solution(C-4) was obtained. After completion of the reaction, the reactionsolution (C-4) was cooled to room temperature, and then poured into a5-times amount of 90:10 hexane-ethyl acetate mixture to result inprecipitation of white powdery matter. This powdery matter was filteredoff, thereby collecting the intended resin (C-4) having the structureillustrated hereinafter.

The polymer's compositional ratio (by mole %) determined by ¹³C-NMR andacid value titration was 32/32/36. Further, the weight-average molecularweight and dispersion degree of Resin (C-4) were found to be 10,000 and2.1, respectively, as measured by GPC and calculated in terms ofpolystyrene.

SYNTHESIS EXAMPLE 5 Synthesis of Resin (C-5)

Methacryloxypropylheptaethyl-T8-silsesquioxane and acrylic acid wereprepared at a ratio of 40 to 60 (by mole), and dissolved intetrahydrofuran, thereby making 450 g of a solution having a solidsconcentration of 50 mass %. To this solution, a polymerizationinitiator, V-65 produced by Wako Pure Chemical Industries, Ltd., wasadded in a proportion of 4 mole %, and this admixture was stirred for 5hours in an atmosphere of nitrogen. Thus, a reaction solution (C-5) wasobtained. After completion of the reaction, the reaction solution (C-5)was cooled to room temperature, and then poured into a 10-times amountof methanol to result in precipitation of white powdery matter. Thispowdery matter was filtered off, thereby collecting the intended resin(C-5) having the structure illustrated hereinafter.

The polymer's compositional ratio (by mole %) determined by ¹³C-NMR was35/65. Further, the weight-average molecular weight and dispersiondegree of Resin (C-5) were found to be 8,500 and 1.8, respectively, asmeasured by GPC and calculated in terms of polystyrene.

In addition, it was possible to synthesize Resins (C-6) to (C-8) inmanners similar to the manner adopted in this Synthesis Example. Theweight-average molecular weights and dispersion degrees of Resins (C-6)to (C-8) determined by measurements of GPC and calculation in terms ofpolystyrene are summarized in the following Table 3.

TABLE 3 Weight-average Dispersion Resin Molecular Weight Degree (C-6)5,900 2.0 (C-7) 6,100 1.9 (C-8) 7,000 1.8

EXAMPLES 1 to 12 AND COMPARATIVE EXAMPLES 1 to 4 Preparation of Resist

Positive resist compositions were each prepared by dissolvingingredients in solvents as shown in the following Table 4 so as toprepare a resist solution having a solids concentration of 7 mass % andpassing the resist solution through a 0.1-μm polyethylene filter.Patterns were formed using each of the thus prepared positive resistcompositions in accordance with a method chosen from those described inTable 5, and evaluated by the following method. Results obtained areshown in Table 4.

[Evaluation of Development Defect]

A defect inspection system, KLA2360 (trade name, made by KLA-TencorCorporation), was used, and measurements with the defect inspectionsystem were made in a random mode under a setting that the pixel sizewas 0.16 μm and the threshold was 20. And development defects extractedfrom discrepancies developing by superposing images for comparison uponpixel units were detected, and the number of development defects perunit area was calculated.

TABLE 4 Composition Acid Basic Pattern Number of Resin (A) generatorResin (C) Solvent compound Surfactant forming defects 2 g (mg) (mg)(ratio by mass) (mg) (mg) method (per cm²) Example 1 9 z2 C-6 SL-1/SL-2N-5 W-1 (A) 0.15  (80) (20) (60/40) (7) (3) 2 1 z51 C-7 SL-2/SL-4/SL-6N-6 W-4 (A) 0.16 (100) (30) (40/59/1) (10)  (3) 3 12 z2/z62 C-5SL-2/SL-4 N-3 W-1 (A) 0.15 (20/100) (150)  (70/30) (6) (3) 4 20 z55/z65C-6 SL-2/SL-4 N-1 W-1 (A) 0.14 (20/100) (30) (60/40) (7) (3) 5 8 z55/z51C-7 SL-3/SL-4 N-6 W-4 (A) 0.12 (20/80) (35) (30/70) (10) (4) 6 20z44/z65 C-3 SL-2/SL-4/SL-5 N-1 W-3 (B) 0.11 (25/80)  (2) (40/58/2) (7)(4) 7 21 z55/z47 C-6 SL-1/SL-2 N-5 W-1 (A) 0.10 (30/60) (15) (60/40)(10)  (4) 8 12 z65 C-7 SL-1/SL-2 N-3 W-2 (B) 0.15 (100) (10) (60/40) (6)(3) 9 8 z44/z65 C-8 SL-2/SL-4/SL-6 N-2 W-3 (A) 0.14 (50/50) (15)(40/59/1) (9) (3) 10  12 z51 C-7 SL-2/SL-4 N-5 W-1 (A) 0.15 (100) (10)(70/30) (7) (3) 11  12 z2/z62 C-8 SL-2/SL-4 N-3 W-1 (A) 0.16 (20/100)(25) (70/30) (6) (3) 12  20 z44/z65 C-6 SL-2/SL-4/SL-5 N-1 W-3 (A) 0.17(25/80) (30) (40/58/2) (7) (4) Comparative Example 1 4 z55/z65 —SL-2/SL-4 N-1 W-1 (A) 2.58 (20/100) (60/40) (7) (3) 2 4 z55/z65 —SL-2/SL-4 N-1 W-1 (B) 2.50 (20/100) (60/40) (7) (3) 3 9 z2 C-6 SL-1/SL-2N-5 W-1 (C) 1.01  (80) (20) (60/40) (7) (3) 4 1 z51 C-7 SL-2/SL-4/SL-6N-6 W-4 (C) 0.88 (100) (30) (40/59/1) (10)  (3)

The characters representing the ingredients in the above Tables standfor the following, respectively.

As to the acid generators, the characters used correspond respectivelyto those standing for the compounds illustrated hereinbefore.

N-1: N,N-Dibutylaniline N-2: N,N-Dihexylaniline N-3:2,6-Diisopropylaniline N-4: Tri-n-octylamine N-5:N,N-Dihydroxyethylaniline N-6: 2,4,5-Triphenylimidazole

W-1: Megafac F176 (produced by Dainippon Ink & Chemicals, Inc., asurfactant of fluorine-containing type)W-2: Megafac R08 (produced by Dainippon Ink & Chemicals, Inc., asurfactant of fluorine- and silicon-containing type)W-3: Organosiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co.,Ltd., a surfactant of silicon-containing type)W-4: Troysol S-366 (produced by Troy Chemical Industries, Inc.)W-5: PF656 (produced by OMNOVA Solutions Inc., a surfactant offluorine-containing type)W-5: PF6320 (produced by OMNOVA Solutions Inc., a surfactant offluorine-containing type)

SL-1: Cyclohexanone

SL-2: Propylene glycol monomethyl ether acetateSL-3: Ethyl lactateSL-4: Propylene glycol monomethyl ether

SL-5: γ-Butyrolactone

SL-6: Propylene carbonate

The pattern forming methods (A) to (D) specified hereinbefore andhereinafter in the tables are set forth in the following Tables 5 and 6.

TABLE 5 Pattern forming method (A) An organic antireflective coatingARC29A (produced by Nissan Chemical Industries, Ltd.) is applied to asilicon wafer, and baked at 205° C. for 60 seconds, thereby forming a 78nm-thick antireflective coating. Thereon, a prepared positive resistcomposition is coated, and baked at 120° C. for 60 seconds, therebyforming a 250 nm-thick resist coating. The thus obtained wafer issubjected to pattern exposure by means of an ArF excimer laser immersionscanner (NA = 0.75) using purified water as an immersion liquid.Immediately after the exposure, water is fed onto the wafer surface toform puddles, and then the wafer is dried by being spun at 2,000 rpm toeliminate the water. Next the wafer is heated at 120° C. for 60 seconds,and then developed with an aqueous solution of tetramethylammoniumhydroxide (2.38 mass %) for 30 seconds, rinsed with purified water, andfurther spin-dried. Thus, resist patterns are formed. (B) An organicantireflective coating ARC29A (produced by Nissan Chemical Industries,Ltd.) is applied to a silicon wafer, and baked at 205° C. for 60seconds, thereby forming a 78 nm-thick antireflective coating. Thereon,a prepared positive resist composition is coated, and baked at 120° C.for 60 seconds, thereby forming a 250 nm-thick resist coating. Theresist coating surface is cleaned by feeding purified water thereto anddrying the water by spinning. The thus treated resist coating issubjected to pattern exposure by means of an ArF excimer laser immersionscanner (NA = 0.75) using purified water as an immersion liquid.Immediately after the exposure, water is fed onto the wafer surface toform puddles, and then the wafer is dried by being spun at 2,000 rpm toeliminate the water. And the wafer is heated at 120° C. for 60 seconds,and then developed with an aqueous solution of tetramethylammoniumhydroxide (2.38 mass %) for 30 seconds, rinsed with purified water, andfurther spin-dried. Thus, resist patterns are formed. (C) An organicantireflective coating ARC29A (produced by Nissan Chemical Industries,Ltd.) is applied to a silicon wafer, and baked at 205° C. for 60seconds, thereby forming a 78 nm-thick antireflective coating. Thereon,a prepared positive resist composition is coated, and baked at 120° C.for 60 seconds, thereby forming a 250 nm-thick resist coating. The thusobtained wafer is subjected to pattern exposure by means of an ArFexcimer laser immersion scanner (NA = 0.75) using purified water as animmersion liquid. Thereafter, the wafer is heated at 120° C. for 60seconds, and then developed with an aqueous solution oftetramethylammonium hydroxide (2.38 mass %) for 30 seconds, rinsed withpurified water, and further spin-dried. Thus, resist patterns areformed.

TABLE 6 Pattern forming method (D) An organic antireflective coatingARC29A (produced by Nissan Chemical Industries, Ltd.) is applied to asilicon wafer, and baked at 205° C. for 60 seconds, thereby forming a 78nm-thick anti- reflective coating. On this coating, a prepared positiveresist composition is coated, and baked at 120° C. for 60 seconds,thereby forming a 250 nm-thick resist coating. Next, pattern exposure isperformed by means of an ArF excimer laser immersion scanner (NA = 0.75)using purified water as an immersion liquid. Immediately after theexposure, isopropyl alcohol is fed onto the wafer surface for 15seconds, and then the wafer is dried by being spun at 2,000 rpm. Herein,the amountt of isopropyl alcohol fed is adjusted to 0.5 kg/cm². And thewafer thus treated is heated at 120° C. for 60 seconds, and thendeveloped with an aqueous solution of tetramethylammonium hydroxide(2.38 mass %) for 30 seconds, rinsed with purified water, and furtherspin-dried. Thus, resist patterns are formed.

It is apparent from Table 4 that the present image forming methods canprovide significant improvements in development defect.

EXAMPLES 13 TO 21

Resists 1 to 6 were each prepared by dissolving ingredients in solventsas shown in the following Table 7 so as to prepare a solution having asolids concentration of 7 mass % and passing the solution through a0.1-μm polyethylene filter. Patterns were formed using each of the thusprepared resists in accordance with the method specified in Table 8,which is either of the methods as set forth in Tables 5 and 6, andevaluated by the same method as in Example 1. Results obtained are shownin Table 8.

TABLE 7 Composition Resin Acid Solvent Basic Resin (A) Generator (ratioCompound (C) Surfactant (2 g) (mg) by mass) (mg) (mg) (mg) Resist 1 23z5 SL-2 N-3/N-5 C-3 W-1 (80) (100) (3/3) (2) (3) Resist 2 24 z5/z55SL-2/SL-4 N-3/N-5 C-3 W-1 (50/50) (60/40) (3/3) (2) (3) Resist 3 25z5/z55 SL-1/SL-2 N-3 C-4 W-1 (50/50) (40/60) (6) (2) (3) Resist 4 26 z5SL-2/SL-4 N-5 C-4 W-1 (80) (60/40) (6) (5) (3) Resist 5 23 z2 SL-2/SL-4N-3/N-5 C-5 W-1 (100)  (70/30) (3/3) (1) (3) Resist 6 24 z2/z55SL-2/SL-4 N-3/N-5 C-5 W-1 (50/50) (70/30) (3/3) (5) (3)

TABLE 8 Pattern Number of forming defects Resist method (per cm²)Example 13 Resist 1 (D) 0.10 Example 14 Resist 2 (D) 0.09 Example 15Resist 3 (D) 0.11 Example 16 Resist 1 (B) 0.12 Example 17 Resist 2 (B)0.11 Example 18 Resist 3 (B) 0.10 Example 19 Resist 4 (D) 0.13 Example20 Resist 5 (B) 0.13 Example 21 Resist 6 (B) 0.13

It is apparent from these results that development defect can beimproved by the pattern forming methods of the invention.

According to the invention, it is possible to provide an image formingmethod which can ensure improvement in development defect appearingafter development in immersion lithography.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

1-12. (canceled)
 13. A pattern forming method which uses a positiveresist composition comprising: (A) a silicon-free resin capable ofincreasing its solubility in an alkaline developer under action of anacid; (B) a compound capable of generating an acid upon irradiation withan actinic ray or radiation; (C) a silicon-containing resin having atleast one group selected from the group consisting of (X) analkali-soluble group, (XI) a group capable of decomposing under actionof an alkaline developer and increasing solubility of the resin (C) inan alkaline developer, and (XII) a group capable of decomposing underaction of an acid and increasing solubility of the resin (C) in analkaline developer, and (D) a solvent, wherein the silicon-containingresin (C) is added in an amount of 0.047 to 6.60 mass % based on thetotal solids in the positive resist composition, and wherein thealkali-soluble group (X) has a phenolic hydroxyl group, a carboxylicgroup, a fluorinated alcohol group, a sulfonic acid group, a sulfonamidegroup, a sulfonylimide group, an (alkylsulfonyl)(alkylcarbonyl)methylenegroup, an (alkylsulfonyl)(alkylcarbonyl)imide group, abis(alkylcarbonyl)methylene group, a bis(alkylcarbonyl)imide group, abis(alkylsulfonyl)methylene group, a bis(alkylsulfonyl)imide group, atris(alkylcarbonyl)methylene group or a tris (alkylsulfonyl)methylenegroup, the method comprising: (i) a step of applying the positive resistcomposition to a substrate to form a resist coating, (ii) a step ofexposing the resist coating to light via an immersion liquid, (iii) astep of removing the immersion liquid remaining on the resist coating,(iv) a step of heating the resist coating, and (v) a step of developingthe resist coating.
 14. A pattern forming method which uses a positiveresist composition comprising: (A) a silicon-free resin capable ofincreasing its solubility in an alkaline developer under action of anacid; (B) a compound capable of generating an acid upon irradiation withan actinic ray or radiation; (C) a silicon-containing resin having atleast one group selected from the group consisting of (X) analkali-soluble group, (XI) a group capable of decomposing under actionof an alkaline developer and increasing solubility of the resin (C) inan alkaline developer, and (XII) a group capable of decomposing underaction of an acid and increasing solubility of the resin (C) in analkaline developer, and (D) a solvent, wherein the silicon-containingresin (C) is added in an amount of 0.047 to 6.60 mass % based on thetotal solids in the positive resist composition, and wherein the group(XI) capable of decomposing under action of an alkaline developer andincreasing solubility of the resin (C) in an alkaline developer includesa lactone group, an ester group, a sulfonamide group, an acid anhydridegroup or an acid imide group, the method comprising: (i) a step ofapplying the positive resist composition to a substrate to form a resistcoating, (ii) a step of exposing the resist coating to light via animmersion liquid, (iii) a step of removing the immersion liquidremaining on the resist coating, (iv) a step of heating the resistcoating, and (v) a step of developing the resist coating.
 15. A patternforming method which uses a positive resist composition comprising: (A)a silicon-free resin capable of increasing its solubility in an alkalinedeveloper under action of an acid; (B) a compound capable of generatingan acid upon irradiation with an actinic ray or radiation; (C) asilicon-containing resin having at least one group selected from thegroup consisting of (X) an alkali-soluble group, (XI) a group capable ofdecomposing under action of an alkaline developer and increasingsolubility of the resin (C) in an alkaline developer, or both (X) and(XI), with the proviso that no group (XII) capable of decomposing underaction of an acid and increasing solubility of the resin (C) in analkaline developer is contained in the resin (C), and (D) a solvent,wherein the silicon-containing resin (C) is added in an amount of 0.047to 6.60 mass % based on the total solids in the positive resistcomposition, the method comprising: (i) a step of applying the positiveresist composition to a substrate to form a resist coating, (ii) a stepof exposing the resist coating to light via an immersion liquid, (iii) astep of removing the immersion liquid remaining on the resist coating,(iv) a step of heating the resist coating, and (v) a step of developingthe resist coating.
 16. A pattern forming method which uses a positiveresist composition comprising: (A) a silicon-free resin capable ofincreasing its solubility in an alkaline developer under action of anacid; (B) a compound capable of generating an acid upon irradiation withan actinic ray or radiation; (C) a silicon-containing resin having (XII)a group capable of decomposing under action of an acid and increasingsolubility of the resin (C) in an alkaline developer, with the provisothat no group selected from the group consisting of (X) analkali-soluble group and (XI) a group capable of decomposing underaction of an alkaline developer and increasing solubility of the resin(C) in an alkaline developer, is contained in the resin (C) and (D) asolvent, wherein the silicon-containing resin (C) is added in an amountof 0.047 to 6.60 mass % based on the total solids in the positive resistcomposition, the method comprising: (i) a step of applying the positiveresist composition to a substrate to form a resist coating, (ii) a stepof exposing the resist coating to light via an immersion liquid, (iii) astep of removing the immersion liquid remaining on the resist coating,(iv) a step of heating the resist coating, and (v) a step of developingthe resist coating.
 17. A pattern forming method which uses a positiveresist composition comprising: (A) a silicon-free resin capable ofincreasing its solubility in an alkaline developer under action of anacid; (B) a compound capable of generating an acid upon irradiation withan actinic ray or radiation; (C) a silicon-containing resin having atleast one group selected from the group consisting of (X) analkali-soluble group, (XI) a group capable of decomposing under actionof an alkaline developer and increasing solubility of the resin (C) inan alkaline developer, and (XII) a group capable of decomposing underaction of an acid and increasing solubility of the resin (C) in analkaline developer, and (D) a solvent, wherein the silicon-containingresin (C) is added in an amount of 0.047 to 6.60 mass % based on thetotal solids in the positive resist composition, and wherein thesilicon-containing resin (C) contains either a repeating unitrepresented by the following formula (C1), or a repeating unitrepresented by following formula (C2):

wherein in formulae (C1) and (C2), XII represents an oxygen atom or—N(R₁₃)—; R₁₃ represents a hydrogen atom, an alkyl group which may belinear or branched and may have a substituent, or a cycloalkyl group;R₁₁ represents a hydrogen atom, a halogen atom, an alkyl group which maybe linear or branched and may have a substituent or a cycloalkyl group;R₁₂ and R₂₁ each represent an organic group having at least one siliconatom, the method comprising: (i) a step of applying the positive resistcomposition to a substrate to form a resist coating, (ii) a step ofexposing the resist coating to light via an immersion liquid, (iii) astep of removing the immersion liquid remaining on the resist coating,(iv) a step of heating the resist coating, and (v) a step of developingthe resist coating.
 18. The pattern forming method according to claim13, wherein the alkali-soluble group (X) has a carboxylic group, afluorinated alcohol group or a sulfonylimide group.
 19. The patternforming method according to claim 18, wherein the alkali-soluble group(X) has a fluorinated alcohol group and the fluorinated alcohol group isa hexafluoroisopropanol group or —C(CF₃)(CF₃)(OH).
 20. The patternforming method according to claim 14, wherein the silicon-containingresin (C) further contains a fluorine atom.
 21. The pattern formingmethod according to claim 15, wherein the silicon-containing resin (C)further contains a fluorine atom.
 22. The pattern forming methodaccording to claim 16, wherein the silicon-containing resin (C) furthercontains a fluorine atom.
 23. The pattern forming method according toclaim 17, wherein the silicon-containing resin (C) further contains afluorine atom.
 24. The pattern forming method according to claim 18,wherein the silicon-containing resin (C) further contains a fluorineatom.
 25. The pattern forming method according to claim 20, wherein thefluorine atom is contained in the form of groups selected from thefollowing categories (F-a) to (F-c): (F-a): alkyl groups having fluorineatoms; (F-b): cycloalkyl groups having fluorine atoms; and (F-c): arylgroups having fluorine atoms.
 26. The pattern forming method accordingto claim 20, wherein the fluorine atom is present in a side chain. 27.The pattern forming method according to claim 20, wherein the fluorineatom is present in the form of either a repeating unit represented bythe following formula (C3) or a repeating unit represented by thefollowing formula (C4):

wherein in formulae (C3) and (C4), X₃₁ represents an oxygen atom or—N(R₃₃)—, wherein R₃₃ represents a hydrogen atom, an alkyl group whichmay be linear or branched and may have substituent, or a cycloalkylgroup; R₃₁ represents a hydrogen atom, a halogen atom, an alkyl groupwhich may be linear or branched and may have substituent, or acycloalkyl group; R₃₂ and R₄₁ each represent an organic group having atleast one fluorine atom.
 28. The pattern forming method according toclaim 21, wherein the fluorine atom is contained in the form of groupsselected from the following categories (F-a) to (F-c): (F-a): alkylgroups having fluorine atoms; (F-b): cycloalkyl groups having fluorineatoms; and (F-c): aryl groups having fluorine atoms.
 29. The patternforming method according to claim 21, wherein the fluorine atom ispresent in a side chain.
 30. The pattern forming method according toclaim 21, wherein the fluorine atom is present in the form of either arepeating unit represented by the following formula (C3) or a repeatingunit represented by the following formula (C4):

wherein in formula (C3) and (C4), X₃, represents an oxygen atom or—N(R₃₃)—, wherein R₃₃ represents a hydrogen atom, an alkyl group whichmay be linear or branched and may have substituent, or a cycloalkylgroup; R₃₁ represents a hydrogen atom, a halogen atom, an alkyl groupwhich may be linear or branched and may have substituent, or acycloalkyl group; R₃₂ and R₄₁ each represent an organic group having atleast one fluorine atom.
 31. The pattern forming method according toclaim 22, wherein the fluorine atom is contained in the form of groupsselected from the following categories (F-a) to (F-c): (F-a): alkylgroups having fluorine atoms; (F-b): cycloalkyl groups having fluorineatoms; and (F-c): aryl groups having fluorine atoms.
 32. The patternforming method according to claim 22, wherein the fluorine atom ispresent in a side chain.
 33. The pattern forming method according toclaim 22, wherein the fluorine atom is present in the form of either arepeating unit represented by the following formula (C3) or a repeatingunit represented by the following formula (C4):

wherein in formulae (C3) and (C4), X₃₁ represents an oxygen atom or—N(R₃₃)—, wherein R₃₃ represents a hydrogen atom, an alkyl group whichmay be linear or branched and may have substituent or a cycloalkylgroup; R₃, represents a hydrogen atom, a halogen atom, an alkyl groupwhich may be linear or branched and may have substituent or a cycloalkylgroup; R₃₂ and R₄₁ each represent an organic group having at least onefluorine atom.
 34. The pattern forming method according to claim 23,wherein the fluorine atom is contained in the form of groups selectedfrom the following categories (F-a) to (F-c): (F-a): alkyl groups havingfluorine atoms; (F-b): cycloalkyl groups having fluorine atoms; and(F-c): aryl groups having fluorine atoms.
 35. The pattern forming methodaccording to claim 23, wherein the fluorine atom is present in a sidechain.
 36. The pattern forming method according to claim 23, wherein thefluorine atom is present in the form of either a repeating unitrepresented by the following formula (C3) or a repeating unitrepresented by the following formula (C4):

wherein in formula (C3) and (C4), X₃₁ represents an oxygen atom or—N(R₃₃)—, wherein R₃₃ represents a hydrogen atom, an alkyl group whichmay be linear or branched and may have substituent, or a cycloalkylgroup; R₃, represents a hydrogen atom, a halogen atom, an alkyl groupwhich may be linear or branched and may have substituent, or acycloalkyl group; R₃₂ and R₄₁ each represent an organic group having atleast one fluorine atom.
 37. The pattern forming method according toclaim 24, wherein the fluorine atom is contained in the form of groupsselected from the following categories (F-a) to (F-c): (F-a): alkylgroups having fluorine atoms; (F-b): cycloalkyl groups having fluorineatoms; and (F-c): aryl groups having fluorine atoms.
 38. The patternforming method according to claim 24, wherein the fluorine atom ispresent in a side chain.
 39. The pattern forming method according toclaim 24, wherein the fluorine atom is present in the form of either arepeating unit represented by the following formula (C3) or a repeatingunit represented by the following formula (C4):

wherein in formula (C3) and (C4), X₃₁ represents an oxygen atom or—N(R₃₃)—, wherein R₃₃ represents a hydrogen atom, an alkyl group whichmay be linear or branched and may have substituent or a cycloalkylgroup; R₃₁ represents a hydrogen atom, a halogen atom, an alkyl groupwhich may be linear or branched and may have substituent or a cycloalkylgroup; R₃₂ and R₄₁ each represent an organic group having at least onefluorine atom.